TOXICOLOGY AND APPLIED PHARMACOLOGY) SUPPLEMENT NO. 3, 30--44 (1969) 

Evaluation of Cosmetics for IrritancyZ 

ALBERT M. KLmMAlq 

Department of Dermatology, University of laennsylvania School of MedieOte, 

Philadelphia, Pennsylvania 29104 

"When description gives way to measurement, 

calculation replaces debate." 

STEVENS 

As with hostility, every one instantly recognizes what is meant by irritancy; nonetheless, our knowledge of these parlous subjects is more descriptive than definitive. 

When we are obliged to provide exact definitions, modes of action, and especially 

appraisals of magnitude, we soon become irritated by ambiguities and vacuities. We 

have in our various roles as toxicologists, lawyers, biologists, physicians, and guarantors of the public weal a keen subjective sense that irritants are harmful, but objective 

criteria for estimating the hazard are hard to come by and in any case controversial. 

Despite these limitations I should like to make it clear at the outset that the general 

record of the cosmetic industry has been very favorable as regards cutaneous toxicity, 

attesting at least to prudence and conservativeness even in the absence of sophisticated 

procedures of testing. 

I do not regard this as an emergency session to straighten out a crooked enterprise. 

Yet it is quite clear that various forces are converging which will necessitate the development of a more reliable and uniform methodology. The distinction between drugs 

and cosmetics, always more casual than correct, must break down under critical 

scrutiny. Surely the thrust of modern technology is toward greater "activity". Enterprising houses are increasingly interested in improving the effectiveness of their products through the opportunities provided by the dazzling inventiveness of the synthetic chemists. Can anyone seriously defend the position that preparations to combat 

acne, dandruff, infections, and excessive perspiration are pharmacologically inactive ? 

Originally cosmetics were designed to conceal or decorate; now we must acknowledge 

that they are often intended to ameliorate or prevent cutaneous abnormalities--dare 

one use the terrifying word "disease" ? In the near future we can expect that cosmetics, 

at least those which influence cutaneous functions, will have to meet the same standards as drugs. This of course means governmental surveillance, and I, for one, think 

the net effect will be salutary, though probably painful. It is no longer adequate to 

depend upon sales as an index of safety. Moreover, the consumer population is more 

disposed toward damaging legal actions, often without real justification. More exacting 

regulations for safety testing will, in the end, protect rather than harass the manufacturers. 

1 This study was conducted under the sponsorship of the Commission on Cutaneous Diseases of the 

Armed Forces Epidemiological Board. 

30 
COSMETIC IRRITANCY 31 

Whereas the primary purpose of a drug is to cure, cosmetics are supposed to delight; 

accordingly, there is practically no tolerance for harmful reactions no matter how 

trivial or transient. The incidence of cutaneous toxicity must perforce be so low as to 

engender insomnia and onyehophagia in those who are ultimately responsible for 

approving the sale of the product. For example, if only one in a thousand users became 

irritated, there would be for every million units sold, a thousand complaints, enough 

to frighten the mamffacturer and alienate the consumer. One cannot too strongly 

emphasize the peculiarly stringent requirements which cosmetics must meet as regards 

irritativeness. In fact the central problem in testing cosmetics is precisely that one is 

generally dealing with products of a very low order of toxicity. Accordingly we shall 

need particularly sensitive techniques of appraisal 

The burden of this discussion is on local irritativeness, not systemic effects. It is my 

intent to sketch out the principles, strategies, and tactics which may be utilized in 

measuring irritativeness. Although a formal consensus does not yet exist, I rather expect that the ideas presented, none of them revolutionary or novel, will accord with 

conclusions that experienced persons generally hold. Because we are just beginning to 

reduce principles to practice, it will be necessary to stress strategies rather than dictate 

tactics. The following script is to be regarded as a framework for the eventual establishment of standards not as a straitjacket to force conformity to a particular method. 

General Prh2ciples 

Irritants are toxic substances which directly damage tissues. This is to some extent a 

definition by exclusion, encompassing all adverse local effects which are nonallergic. 

Simple as it is, the subject is confounded by curious notions and an archaic nomenclature. For example, it is the convention to place the adjective "primary" before the 

term irritant so that one speaks about "primary irritants." The strict semanticist will 

then wish to know how these differ from "secondary" or even "tertiary" irritants. It 

has been suggested that "primary" irritants irritate on the first exposure and secondary 

irritants after multiple exposures, but this leads to the complication, if not contradiction, that a substance may be both a primary and a secondary irritant depending on 

concentrat~o~ alone (Shelanski, 1951). The term primary irritant is a misconception; 

"primary" is redundant, and its permanent expulsion will encourage clearer description and more rigorous thinking. 

Far more serious is the tradition, glaringly visible in teaching texts, of dividing substances into two classes, irritants and nonirritants, implying that one need only consult 

an authoritative list to decide whether a substance is likely to be harmful or not. This 

is not merely an oversimplication, it is specious in the extreme. No substance is always 

safe, nor ahvays harmful. The distinction we are after is quantitative not qualitative. All 

substances are potential irritants. They may vastly differ in degree of irritativeness, but 

recognizing the principle has the beneficial effect of compelling us to think in forms of 

"how different" ? We can answer this only by a measurement of some kind, and such 

measurement is obtainable only by procedures which are susceptible to quantitation. 

The goal then becomes a rigorously defined methodology which will yield figures that 

can be treated statistically. 

My insistence that all substances should be regarded as potentially irritating is by 

no means an academic doctrine. If we take the instance of water, the "harmless" 
32 KLIGMAN 

substance pat" excellence, we can nevertheless envision situations in which the effect is 

harmful. For example, keeping the skin wet under occlusive dressings or by prolonged 

immersion can readily lead to closure of the sweat pores provoking sweat retention 

lesions of miliaria. Or, the enormous stimulus to bacterial and fungal growth furnished 

by wetness and hydration of the horny layer may elicit pyoderma or moniliasis. 

Admittedly the mechanism of injury is indirect, but the consequences are harmful 

nonetheless. In any case, these peculiar reactions will have to be taken into account 

when interpreting closed patch tests under which hydration is unavoidable. In hot 

weather miliaria is easily mistaken for an irritant reaction. So for that matter are 

staphylococcal infection and moniliasis. Each of these false positive expressions has led 

me into error, indeed with such frequency that one ought constantly to maintain a 

high index of suspicion. 

Still another erroneous notion is that individual differences in susceptibility to irritation are not thought to be very great. It is usually taught that only a proportion of 

the population is likely to become allergic to a sensitizer whereas all persons will react 

to an irritant. This is a false conception which comes about because of the unconscious 

tendency to think that irritants are strong and allergens mild. However, one could 

argue the opposite case. For example, with potent allergens such as p-phenylenediamine or tetrachlorosalicylanilide all adequately exposed persons will become sensitized. By contrast with weak irritants such as 1 ~o hexachlorophene in mineral oil or 

Hydrophilic Ointment U.S.P. (containing 1 ~ sodium lauryl sulfate), no amount of 

exposure is ever likely to prove irritating to more than a small proportion. In this 

instance, the difference between irritants and sensitizers is not quantitative but qualitative. The frequency of reactions cannot help one decide whether one is dealing with 

one rather than the other, not to mention the complication that many substances are 

both. 

Even experienced persons sometimes do not appreciate the vast inherent differences 

in susceptibility to irritation. This is because data have usually not been collected 

under sufficiently rigorous conditions to enable one to plot frequency distributions and 

obtain an idea of dispersion. Everyone recognizes that some persons react more swiftly 

or more intensely than others, but adequate characterization of subject variability 

requires some kind of dosage response data. For detergents, Justice et al. (1961), in 

arm immersion tests and Kligman and Wooding (1967), using patch tests with a variety 

of irritants, have demonstrated that the log normal probability plot is, in fact, linear. 

The slope may be shaIlow and the dispersion great, indicating marked individual 

variation. To emphasize this point I have collected some new data for the express purpose of presenting them in the form of a frequency distribution plot. It should be noted 

that the data are probably more reliable than usual because the subjects were of the 

same age and race (20- to 25-year-old, white males), all the testing was done at the 

same time, and one person applied all the patches according to a rigid routine. A 20 

aqueous solution of aluminum sulfate was applied under continuous occlusion for 12 

days to a forearm site of 100 males. The dressing was changed every other day, the 

solution being reapplied to the same site by our standard technique (Kligman and 

Wooding, 1967). For each subject the end point was the number of days just required 

to produce an erythema, after which there was no further exposure. Figure 1 is a frequency distribution bar plot based on percentage of persons reacting at 2, 4, 6, 8, 10, 
COSMETIC IRRITANCY 33 

or 12 days. Naked-eye inspection is sufficient to establish that the pattern more or less 

approximates a normal, bell-shaped distribution curve although there is some skewness. Clearly, individuals differ with respect to the amount of exposure that will cause 

irritation, in some in as little as 2 days and in others 12. The majority react by 6 days. 

Failure to appreciate the range over which the irritancy data may be spread promotes 

misinterpretations. This problem arises, for example, when one wishes to establish a 

nonirritating concentration for allergic patch testing. Large numbers of subjects must 

be studied to establish safe levels. Suppose that only 5 ~ react to a concentration which 

is harmless for the rest of the population. One might patch test 25 subjects and find no 

reactors at this concentration. In future patch tests with this "safe" concentration, 

reactors would be deemed allergic. There are instances in which patients were judged 

30 

~o 

I0 

7 2ox At2 (so,)~ 

2 4 6 8 I0 12 

Days 

Fro. 1. Frequency distribution of the days required to just produce redness in 100 males patchtested continuously with 20~ aluminum sulfate for 12 days. 

to be contact-sensitized to propylene glycol and ammonit~m persulfate solely because 

they reacted to concentrations which are usually harmless (Warshaw and Herrmann, 

1951; Calnan and Shuster, 1963). 

The most thorough quantitative study of reactions to a variety of irritants has 

recently been published as a doctoral dissertation by BjSrnberg (1968) in Sweden, 

Among many valuable results was the finding that individuals cannot be characterized 

as being more or less generally susceptible to irritation. High susceptibility to one 

irritant is poorly correlated with susceptibility to another. Each irritant is a case unto 

itself and cannot serve to locate individuals at unusually high risk of irritation. Thus 

pro-employment patch testing is probably irrational. 

The universe of chemicals is multitudinous and multifarious. It would be decidedly 

helpful if we had a better understanding of the mode of action of irritants, i.e., the biochemical and pharmacologic events which lead to an inflammatory response. Unfortunately our ignorance of this subject is profound except for the obvious example of 
34 KLIGMAN 

that class of extremely toxic substances which physically degrade the structural components and macromolecules of cells, sometimes lumped together under the term of 

caustics. Strong acids and bases will hydrolyze or coagulate proteins, rendering the cell 

lifeless. Coming down the scale, anionic surfactants and even urea will denature proteins and arrest metabolic function. Dimethyl sulfoxide makes cell membranes so 

permeable that the vital disequilibrium between the external and internal milieu cannot be maintained. Lysosome labilizers, such as vitamin A, probably excite damage 

through the release of proteases and acid hydrolases, a more subtle mode of action. 

Some chemicals provoke urticarial reactions by releasing histamine fi'om mast cells. 

Other possible effects include enzyme inhibition, complexing of DNA and RNA, and 

mitotic inhibition. However, as regards the mode of action of most mild irritants, we 

are mainly in the dark. This is a basic biological problem which has yet to be vigorously attacked. That irritants cause very different types of damage becomes obvious 

when the injured tissue is examined microscopically. Figures 2A to 2I illustrate the 

variability of the histologic injury. 

Still another problem concerns the clinical criteria by which contact allergy and 

irritancy can be differentiated. The classical signs of dermatitis are chiefly redness and 

swelling, sometimes accompanied by oozing and blistering. However, these manifestations are stereotyped, common reactions to injury. Though the experienced observer 

can often grossly distinguish irritation from sensitization when the reactions are 

severe, this is definitely not true of mild responses which may consist only of redness 

and slight swelling. Clinical powers fail utterly. This difl]culty is not simply something 

for scholars to worry about. With the Draize-Shelanski repeated insult test I have too 

often been mistaken in diagnosing irritancy reactions as allergic and vice versa on the 

~.,,~o ;'4" "2 

i~i~lll~ r ;, 9 ~ ~.t.~' , _,-, . ,,,,,- . 

"l",'~Ik3W" ~ 

, ~"" ,. ~ .~ " t*-~ ,'~".~"r " ~. :~, 

FIG. 2. Variations in response of human cutaneous tissue to different irritants. Hematoxylin 

and eosin. (A) Cantharidin, intraepidermal blister; the primary event, before cellular damage, is a 

loss of cohesion between the cells so that they simply fall apart and float freely in the cavity. • 
COSMETIC IRRITANCY 35 

Fio. 2 (B) Thickened, hyperplastic epidermis, covered with a crust of killed cells, 4 days after 

application of a cationic detergent, x I 11. 

~7~37;; ... . / . 

FIG. 2 (C) Follicular abscess following application of high concentration of a corticosteroid, x45. 
36 KLIGMAN 

FIG. 2 (D) Infiltration of leukocytes around intraepidermal sweat duct following application of 

aluminum sulfate. :<360. 

2(X) 

F1o. 2 (E) Subcorneal blister with toxic epidermal changes due to kerosene, x 129. 
COSMETIC IRR[TANCY 37 

...... ~ ' ~" ~ -41- "~ - ~ 

Fzo, 2 (F) Subepidermal blister due to sodium lauryl sulfate. The epidermis is surprisingly normal. 

• 159, 

FIo. 2 (G) Intercellular edema induced by vitamin A acid, a lysosorne ]abilizer. The cells are forced 

apart by fluid, accentuating the prickles. • 
38 KLIGMAN 

"2(H) ' " ..,V ~" 

N 

"O 

III ," 

Fro. 2 (H) Follicular abscess due to croton oil. x I t I. 

~~,~ . ~' 

'S 

! ) Nt~ 

Fro. 2 (I) Complete destruction of epidermis and necrosis of dermis produced by a caustic application of sodium hydroxide, x219. 

final challenge patch test. The only recourse I know of for resolving this issue confidently is biopsy. A 3 mm punch will do. The histologic pattern of the allergic reaction 

is diagnostic, beginning with perivenular accumulations of mononuclear cells accompanied by exocytoses of lymphocytes and spongiosis. 
COSMETIC IRRITANCY 39 

So'ategies for Appraising b'ritants 

While it is obligatory to use human skin for final evaluation, one should not on that 

account discount the usefulness of animal bioassay in preliminary screening. As a rule, 

the depilated skin of rabbits and guinea pigs is more easily irritated, but this can hardly 

justify a surprisingly widespread anthropocentric bias against animal tests. On the 

contrary, careful comparative study on both human and animal skin shows quite 

clearly that the rank order ofirritancy may be much the same (Justice et al., 1961 ). 

It must be emphasized that irritancy testing is afflicted with numerous variables 

whose influence must be minimized. These are too easily disregarded except by those 

who have suffered the torment of trying to obtain reproducible results. Cutaneous reactivity is influenced by body region (the scalp and face are comparatively resistant), 

age (children are more easily irritated), sex ([imited evidence suggests a slightly greater 

susceptibility for women), and type of test (closed patch testing is decidedly more 

irritating than open). Season must also be considered although with closed patch testing the conditions are really equivalent throughout the year. In daily l-hour arm immersion tests, the skin is unquestionably more reactive in winter than summer, 

although the contrary impression is widely held. Justice et al. (1961) showed this for 

surfactants, and we too have demonstrated greater winter reactivity for a variety of 

irritants. To obtain equivalent degrees of irritancy in summer it may be necessary to 

almost double the concentration. 

In any case, irritancy data are valid only when the conditions are precisely specified. 

Even so, there remain trying technical problems which adversely affect accuracy and 

reproducibility. At present, it is unwise to suppose that the most exacting procedures 

yield values which have anything like the accuracy of clinical laboratory tests such as 

the serum cholesterol, glucose tolerance, or urinary ketosteroids. The most meticulously executed irritancy test yields values which are best regarded as relative rather 

than absolute. We must perforce rely on comparative evaluations. For example, in a 

two-way comparison of products A and B, our currelat methods are adequate to decide 

whether A is significantly more irritating than B, less irritating than B, or indistinguishable. When a score of formulations are compared, those can usually be satisfactorily 

ranked in their order of irritancy. As a consequence, the products to be compared 

must be tested on the same subjects at the same time. 

As a matter of fact, comparative data are really quite reliable if one makes judicious 

use of slandards of reference. These are formulations or materials whose safety record 

is already known after widespread usage over a period of years. The usage history is a 

valuable item of information which can effectively be coordinated with the bioassay 

results in prognosticating toxicity. The first requirement is that the comparisons be 

between similar products: hand creams with hand creams, not with remedies for athletes foot; antiperspirants with antiperspirants, not with anti-dandruff proprietaries. 

The physical status should be the same, viz, liquids with liquids, etc. By the device of a 

reference standard, the artificial conditions of bioassay may be related to actual usage. 

To be feasible, bioassay must furnish accurate irritancy appraisals with small 

groups of test subjects. The objective is to obtain assessments in, say. 10 test subjects 

that would otherwise require perhaps 1 to 10,000 users to provide. Since with cosmetics we will usually be dealing with formulations of very low toxicity, this objective 

can be attained only by tremendously magnifying or exaggerating the test exposures. 
40 KLIGMAN 

The conditions of bioassay bear no resemblance to actual usage, and it must be stressed 

that the proportion of subjects irritated by the test system gives no direct indication of 

the probable incidence of irritation in the user population. 

Since the details of our basic methods have already been published (Kligman and 

Wooding, 1967), it wilt suffice here to outline our general approach. What I wish to 

emphasize is not the technical specifications, which will probably be modified anyway 

as experience develops, but rather the strategies that can be used to compare irritativeness. 

We use small groups, usually 10 adults. Caucasians are preferable, but the experienced worker may utiIize more pigmented subjects. Theoretically two irritancy parameters can be quantitated: (1) the proportion of subjects who react (frequency data) 

and (2) the degree of reaction (intensity data). Appraising intensity is a highly subjective and uncertain business with built-in vagaries. The most important of these is the 

diversity of the inflammatory expressions of different irritants so that uniform scoring 

becomes quite impossible. Many workers do not appear to be seriously troubled by 

the fact that above the erythema threshold, irritants do not behave the same way. As 

the reaction becomes stronger, a variety of pictures may develop. We have simply been 

unable to force our observations into the conventional 4-point scale, so blithely 

described in the literature: viz, +, erythema; ++, deeper erythema and swelling; ++% 

the foregoing plus vesicles or papules; ++++, the addition of bullae and crusting. 

Unfortunately many strong irritants never produce vesicles or bullae but simply kill 

the epidermis outright so that one gets necrosis, erosions, or ulceration without going 

through a blistering phase. Some irritants elicit pustules or induce suppuration. 

Among other possible manifestations are bloody, suppurative or serious oozing, 

various types of crusts, scaling, etc. Eight-point scales have been published in which 

the intensity of erythema alone is graded over a 4-point range. Our main criticism of 

such scoring systems is not that they cannot be successfully used by skilled observers, 

but rather that different workers are not likely to obtain comparable results. We have 

resolved this particular problem by ignoring it: we make no effort to grade intensity. 

Instead, we use procedures which simplify interpretation by allowing the observer only 

one choice. Either uniform erythema is present or not; this is somewhat similar to the 

minimum erythema dose (MED) utilized to estimate the effect of ultraviolet radiation. 

The use of a quantal, all-or-none, decision increases reproducibility and greatly 

diminishes observer variability. 

It turns out that the accuracy of the test increases with the potency of the irritant. It 

is comparatively simple to appraise strong irritants which are capable of causing a reaction within 24 hours in all subjects. The statistic utilized is the ID50: the concentration that will cause an erythema by occlusive patch testing in 50 ~o of the subjects. 

Various dilutions are employed over an appropriate range determined by preliminary 

testing; an effort is made to obtain a good scatter. At the highest concentration 

90-100 ~o should react, and 0-10 ~o at the lowest. The percentage of subjects reactive 

to each concentration is plotted on log normal probability paper. A straight line is 

visually fitted and the ID50 is read off the graph. By means of the Litchfield-Wilcoxon 

method of probit analysis, one can establish the 95 ~ confidence limits of the ID50, 

the slope function and its confidence limits, and assess the statistical significance of the 

differences between irritants. One should note that substances which have identical 
COSMETIC IRRITANCY 41 

ID50 values are not necessarily of equal irritancy unless their slope functions are also 

the same; the one with the steeper slope is the stronger irritant. 

For chemicals or formulations of moderate irritancy it is necessary to reapply the 

patch at the same site daily for 10 days, the end point being the number of days that 

will produce an erythema. When this is reached no further patches are applied to that 

site. The cumulative percentage of reactors per day is plotted against days on log 

normal probability paper as above (Fig. 3), The statistic provided in this case is the 

99.99 

99.9 

99.S 

99.5 

99 

98 

95 

90 

SODIUM THIOGLYCOLLATE, 20% 

TIME- RESPONSE LINE 

ITE4= 9.4 days 

80 B 

Z 70 - 

60 - • 

0 IT50 = 5.2 days 50 

40 -- X 

20 -- ITI6 ~ 2.9 days 

~ ~o0.2 

0.I 

0.01 

1 2 3 4 5 6 7 8 910 20 30 40 50 607080 

CUMULATIVE EXPOSURE TIME, d:,ys 

Flo. 3. Log probit plot of the cumulative percentage of daily reactors in a 10-day continuous patch 

test with sodium thioglycolate, The straight line represents the best visual fit; the IT50 is then directly 

read off. 
42 KLIGMAN 

IT50, the number of days requi red to just produce redness in 50 ~ of the subjects. The 

data are treated in the same way. With mildly irritating substances it may be necessary 

to extend the daily exposures to 20 days in order to exceed a 50 ~o reaction rate. Though 

one might expect otherwise, it often happens that increasing the number of days fails 

to raise the reaction rate materially; for example if only 20~ react by the end of 10 

days, another 10 days' exposure does not necessarily recruit additional reactors. With 

mild irritants it is almost characteristic for the cumulative response curve to level off 

within a week or so. 

The Scotch Tape Stripping lrritancy Test 

The publication by Kligman and Wooding (1967), was limited to a description of 

the ID50 and IT50 procedures. These methods have an important limitation: when the 

product or substance fails to induce reaction rates in excess of 50%, the IT50 or 

ID50 values cannot be reliably determined and the benefits of statistical analysis are 

lost. Regrettably, it turns out that these procedures are often inapplicable to cosmetics. A different strategy must be employed, to further magnify the exposure. The 

principle is similar to that used by Finkelstein et aI. (1963) in animal testing. It entails 

mildly damaging the skin by chemical or physical means. The insult must be sufficient 

to disrupt the horny layer barrier and thus enhance the penetration rate. We tried 

various means of injury and finally decided on Scotch tape stripping, mainly because 

it can be precisely controlled, guarantees total removal of the barrier, and induces a 

uniform but mild inflammation. Our experience is still too limited to lay down rigorous 

rules, but the results to date are promising enough to justify a tentative description of 

the method. Since stripping itself induces some inflammation, one is obliged to forego 

quantal responses and to evaluate the intensity of the reaction. On stripped sites, even 

mild irritants will intensify inflammation. Obviously a Scotch tape stripping control, 

treated only with the vehicle, must be included. The sites are prepared by stripping to 

the glistening layer, using a uniform stripping technique. The material is applied continuously under occlusion once daily, generally for 5 days--less if great differences 

become apparent. We find that the intensity generally reaches a maximum by 3-5 days 

and the skin then tends to recover regardless of further exposure. Intensity is arbitrarily 

scored on a 5-point scale by comparing the response to the control. Ten subjects are 

utilized, and the intensity readings are averaged for each day. Only experience can 

instruct the observer regarding rating of the reaction. Needless to say, this is a technical weakness of the test, and different observers are likely to score the reactions 

differently. With a suitable reference standard, however, a given observer can still 

reliably discriminate among weak irritants of differing irritancy potential. The usefulness of the procedure may be illustrated by a comparison among a homologous series 

of straight-chain fatty acids. In 2 ~o concentration in mineral oil, these mimic many 

cosmetics in that their continuous occlusive application to normal skin for 10 days 

generally produces no reactors. Fatty acids were selected because it has been established that irritancy increases with chain length to a maximum at C12 and tends to fall 

thereafter (Kooyman and Snyder, 1942; Kellum, 1968). Figure 4 shows the results 

obtained by the stripping technique for even-numbered fatty acids from C8 to C14, 

The comparative irritancies agree with the published results, attesting to the validity 

of the method. Means of handling these data statisticalIy have still to be worked out. 
COSMETIC IRRITANCY 43 

3 

2% FATTY ACIDS 

~- .... xcl4 

A,---. __m C 12 

o ........ o CIO 

,i---- --A C 8 

o--------~ C 6 

..__.---- _ rj. 

---j..j 

~ I =,1 ;L 

I 2 ~ 4 

Days 

FiG. 4. Appraisal of the comparative irritancy of fatty acids by the Scotch tape stripping method. 

Toxicity increases with increasing chairt length to a maximum at Cz2. The separation is greatest at 2 

days. 

Techniques of Patch Testing 

These bioassays uniformly use occlusive patch tests, the details of which have been 

published elsewhere (Kligman and Wooding, 1967). Certain key points are worth reviewing and emphasizing. 

No test, of course, is worth the trouble if it is slovenly executed. It is the peculiar pitfall of the patch test that one may commit sins without realizing the transgression. The 

danger is that the patch test is beguiIingly simple. Its basic mechanics are easily learned. 

One loads the patch and seals it to the skin with adhesive. However, it is the state of 

the patch within the next 24 hours which is crucial. No warning is needed that the test 

is invalidated if the patch comes off or is grossly loosened. Yet it is surprising how often 

the results are vitiated because of seemingly slight changes in the physical status of the 

patch. This occurs so frequently that it tends to be accepted as unavoidable, [ am referring to partial loss of occlusion. Occlusion is absolutely essential in achieving reproducible results. The occlusive patch is a device to provide continuous, uniform, intimate contact with the skin. This is not easy to achieve because the subjects are not 

immobilized and their normal physical activity stretches and deforms the skin. 

Movements during sleep can easily distort patches on the back. In a regional comparison Magnusson and Hersle (1965), thought the latter area was slightly more reactive because of pressure during sleep. The commonest type of loss of occlusion is 

wrinkling and folding of the patch. How many of us would be willing to let an outside 

observer examine our next hundred subjects for integrity of the patch 24 hours after 

placement? Scrupulousness in applying patch tests so that they truly remain occlusive 

for 24 hours is by far the most decisive factor in achieving reliability. 

Our patches consist of 1-cm squares of Webril (Curity), a highly absorbent nonwoven fabric. The patches are loaded with a uniform quantity of the test solutions, 

cream or ointment from a tuberculin syringe. The patch is held to the skin under overlapping strips of impermeable plastic tape (Blenderm, 3M). Finally this arrangement is 

reinforced by overlapping longer strips of tape. A common error is to indulge the 

natural inclination to keep the entire dressing small. The strips of impermeable tape 
44 KLIGMAN 

directIy over the cloth should be at 1east 2 inches long and the final outside tape at/east 

3 incites long. These specifications may of course be individualized. 

Determination of erythema thresholds is more greatly influenced by lighting than 

one might suppose. Fluorescent bulbs rich in blue light are especially handicapping. 

We use sunlight-mimicking light (Macbeth Corp., Newburgh, New York). 

If possible, the summer months should be avoided. No dressing is secure in a stream 

of sweat. 

It has been reported that repeated patch testing leads to a gradual increase in skin 

irritability, resulting in abnormally high reaction rates even when completely different 

sites are used each time (van Haam and Mallette, 1955). Dermatologists generally 

believe that the skin becomes hyperirritable in the presence of a widespread dermatitis, 

but except for Bj/3rnberg's (1968) suggestive results, I know of no telling proof. Indeed, 

I have repeatedly tried to confirm this nonspecific increase in irritability without success. For example, if a severe dermatitis on both forearms is induced by daily immersions in irritating chemicals the ID50 values on the back at the very height of inflammation were not found to be different from the preexposure figure. In addition we have 

repeatedly used the same subjects for testing strong irritants over a period of several 

months, without noticing any change in skin susceptibility. I am of the opinion, therefore, that when one has assembled a cooperative panel of test subjects, these can be 

used indefinitely. It is probably a sound precaution to leave several weeks between 

tests and to avoid sites previously irritated. 

REFERENCES 

BJrRNB~RO, A. (1968). Skin. Reaetio1~s to Primary Irritants in Patients with Hand Eczema. 

Doctoral thesis. Oscar Isacsons Tryckeri, Goteburg, Sweden. 

CA.LNAN, "D. C., and SRUSTeR, S. (1963). Reactions to ammonium persulfate. Arch. Dermatol. 

88, 12. 

FnqKLESTEIN, P., LADEN, K., and MIECHOWSKI, W._(1963). New methods for evaluating cosmetic irritancy, a v. h~vest. DermatoI. 40, 11. 

JUSTICe, J. D., Te, hVERS, J. J., and VrNSON, L. J. (1961). The correlation between animal and 

human tests in assessing product mildness. Proc. Sci. Sect. Toilet Goods Assoc. 35, 12. 

KELLUM, R. E. (1968). Ache vulgaris. Relative irritancy of four fatty acids from C12 to CI6. 

Arch DermatoL 97, 722. 

Kt.x~MA~q, A. M., and WOODING, W. M. (1967). A method for the measurement and evaluation of irritants on human skin. J. hwest. Dermatol. 49, 78. 

KOOYMAN, D. J., and StqvDta, F. A. (1942). Tests for the mildness of soaps. Arch. Dermatol. 

46, 846. 

MAGNUSSON, B., and HE~SLE, K. (1965). Patch test methods. II. Regional variations of patch 

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