Environmental Health Perspectives

Vol. 94, pp. 91-94, 1991

Irritant Effects of Formaldehyde Exposure

in Mobile Homes

by Kai-Shen Liu,* Fan-Yen Huang,* Steven B. Hayward,*

Jerome Wesolowski,* and Ken Sextont

This paper reports the irritant effects associated with formaldehyde exposures in mobile homes. Week-long, integrated

fomakldehy concentratioas were nm red uing paive monitors insummer and winter while the mobile home residents

continued their normal activities. Information on acute health problems, chronic respiratory/allergic illnesses, smoking

behavior, de v , and time spent at home was obtnedon over 1000 individuals during the sampling period.

Measured formaldehyde concentrations varied from under the limit of detection (0.01 ppm) to OA6 ppm. Formaldehyde

exposure was estiated for each individual by multiplying the concentration measured in his or her home by the time he

or she spent at home. Irritant effects were found to be associated with formaldehyde exposure after controlling for age,

sex, smoking status, and chronic illnesses using a logistic procedure. Some of the interaction terms found to be significant indicated that there were synergistic effects between formaldehyde exposure and chronic health problems.

Introduction

Acute health effects caused by low-level exposures to formaldehyde (HCHO) have been demonstrated in controlled

studies of humans and animals and have also been observed in

occupational and residential environments (1). Human subjects

have experienced eye irritation at 0.5 ppm in an experimental

chamber (2). Irritation effects in the upper respiratory tract begin

at 0.1 ppm and become more common at 0.2 ppm (3). Symptoms

in the lower airways such as cough, chest tightness, and wheeze

are observed at higher levels (> 5 ppm), but may occur in the

presence of fine particles at lower (0.07 ppm) concentrations

(4,5). Electroencephalogram (EEG) changes have been found in

human subjects exposed to 0.04 ppm of HCHO (6 ). Headache,

nausea, vomiting, and diarrhea have been reported by people exposed to concentrations ranging from 0.02 to 4.15 ppm in residential environments (7). Neurobehavioral effects, such as

headache, dizziness, nausea, memory loss, and sleeping problem were also observed amoi1t histology technicians exposed

to concentrations between 0.2 and 1.9 ppm (8).

Approximately 1 to 7% ofdermatologic patients show positive

responses to patch tests with 2% HCHO (9). While it is clear that

HCHO can produce hypersensitivity reactions by the dermal

route, it is less certain that it can induce hypersensitivity reactions

by inhalation (bronchial asthma). Occupational studies have

*California Indoor Air Quality Program, Air and Industrial Hygiene Laboratory, California Departmntof Health Services, 2151 Berkeley Way, Berkeley,

CA 94704-9980.

tOffice of Health Research, RD-683, United States Environmental Ptection

Agency, Washington, DC 20460.

Address reprint requests to K. -S. Liu, California Indoor Air Quality Program,

Air and Industrial Hygiene Laboratory, California Department of Health Services, 2151 Berkeley Way, Berkeley, CA 94704-9980.

shown that bronchial asthma is related to repeated exposure to

HCHO at levels lower than 1 ppm, even though chamber studies

have failed to produce asthma attacks in nonasthmatic people, or

even on asthma patients at higher levels (10,11). The reason for

the discrepancy between the occupational finding and the results

of chamber studies is not known.

Since formaldahyde is an irritant chemical that also causes

hypersensitivity reactions, it is possible that it might produce

more symptoms among people with chronic respiratory illnesses

and allergy problems. But aside from the investigations ofasthma

patients mentioned above, there are no systematic studies on

HCHO's effects on people with chronic respiratory diseases or

allergy problems.

HCHO is a widely used chemical. Billions of pounds of

HCHO are produced in the United States annually, ofwhich approximately one-half is used in the wood products industry.

Plywood and particle board, commonly used in construction, are

the major sources of HCHO in residential environments. Mobile

homes, because of their air-tight structures, extensive use of

pressed wood products, and relatively small volumes are more

likely to have elevated HCHO concentrations than conventional

homes. HCHO-related health complaints in mobile homes have

been reported in several states (12), and several investigations

have been carried out to study such complaints. A random sample of mobile homes has been investigated in only one study,

namely, a pilot study of 65 noncomplaint mobile homes in

Wisconsin. In that study, a positive relationship was found between HCHO concentration and eye irritation (13). However,

due to the small sample size, only one of many potential confounders, age, was adjusted for in the statistical analysis.

In 1984-1985, the California State Indoor Air Quality Program

carried out a random survey ofHCHO in mobile homes. The major hypothesis to be tested was that irritant effects are positively
LIUETAL.

associated with HCHO exposures. To test the hypothesis, the

survey was designed to a) obtain the distribution of HCHO

concentrations from randomly selected noncomplaint mobile

homes, b) estimate HCHO exposures for residents of mobile

homes using the concentration data and time activity patterns for

occupants, and c) test the association between HCHO exposures

and physical symptoms by controlling major potential confounders. The survey was also used to determine the important

factors affecting HCHO concentrations. This paper addresses

mainly the health effects of HCHO, while previous papers

discussed other aspects of the study (14-17).

Methods

An age-stratified random sampling scheme was used in this

survey for the selection of mobile homes. A list of randomly

selected mobile homes with approximately 60% of the homes

manufactured after 1980 was provided by the California Department of Housing and Community Development. Atotal of2203

letters were mailed to recruit participants. Forty-four percent of

the recipients responded positively to the request, and the age

distribution oftheir residences was similar to that ofthe original

list. The survey consisted of two phases. The summer phase was

carried out during July and August, 1984, and the winter phase

during February and March, 1985. A total of663 mobile homes

with 1394 residents completed the summer phase and 523 homes

with 1096 residents finished the winter phase of the survey. A

detailed description ofthe study design can be found in a previous

publication (14).

The large sample size of the participants (over 1000 individuals) allowed for control of potential confounders such as

age, sex, smoking status, and time spent at home without the loss

of statistical power. It also allowed the investigation ofthe effects

of HCHO on people with chronic respiratory illnesses and

allergy problems.

This survey was carried out by mail, although approximately

20% ofthe residences were visited in the summer, and an additional 14% were visited in the winter. Passive HCHO monitors,

along with a cover letter, instructions, logging forms, a questionnaire, and a return envelope were mailed to the participants. They

were instructed to uncap the monitors and put one in the kitchen

and one in the master bedroom. After 7 days of exposure,

monitors and completed questionnaire were mailed back. The

residents carried out their normal daily activities during the

monitoring period. HCHO concentrations were measured using

the chromatrophic acid method.

The survey questionnaire consisted of questions on housing

characteristics, household activities, and occupant information.

It was filled out by an adult in each participating household. Occupant information was obtained for all residents. It included personal data, presence or absence of 6 respiratory/allergy diseases,

and 16 physical symptoms. Personal data requested were name,

age, sex, occupation, smoking status, and the average number of

hours spent at home per day during the 1-week monitoring

period. Individual exposure was obtained by multiplying the

average HCHO concentration by the time spent in the mobile

home. The 6 chronic conditions were asthma, hay fever, emphysema, rashes, chronic bronchitis, and allergies. The 16 symptoms were asthma attacks, wheezing or difficult breathing, chest

pain, stinging or burning skin, burning or tearing eyes, sore

throat, running nose, cough, rashes, headache, sleeping problems, dizziness, nausea or vomiting, unusual fatigue or

drowsiness, abdominal pain, and diarrhea. Occurrences ofthese

symptoms were reported for the 2 weeks prior to the end of the

monitoring period.

Variables related with symptoms were first identified using

univariate analyses. The effects of HCHO on symptoms were

then evaluated using logistic regression to control potential

confounders.

Results

HCHO concentrations measured in this study varied from

below the limit of detection (0.01 ppm) to 0.46 ppm. Since no

significant differences were found between the kitchen and

bedroom measurements, the two values were averaged to represent the whole-house concentration. The mean of the wholehouse HCHO concentrations of all monitored mobile homes was

0.089 ppm inthe summer and 0.088 ppm in the winter. The weekly HCHO exposure for each individual was obtained by multiplying the whole-house concentration by the total number of hours

spent at home during the monitoring week. Weekly HCHO exposures varied from 0 (several residents did not stay at home during the sampling week) to 53.4 ppm-hr in the summer and from

0 to 40.9 ppm-hr in the winter. The average exposures were 9.8

ppm-hr and 9.9 ppm-hr, respectively.

Based on the returned questionnaires, there were 1394 individuals included in the summer phase and 1096 individuals included in the winter phase ofthe study. The characteristics ofthe

participants are shown in Table 1. Fifty-three percent were

females and 47% were males. One-third were 65 years ofage or

older, and one-quarter were smokers. Thirty-three percent

reported having chronic respiratory disease and/or allergy

problems.

The symptoms reported in this survey were found to be

statistically significantly related with gender, age, smoking

status, and presence ofchronic respiratory/allergy problems. As

can be seen in Tables 2 and 3, the percentage of people having

various symptoms was generally higher for females, smokers,

and persons with chronic respiratory/allergy problems.

However, the reported symptoms did not vary linearly with age.

When the prevalence ofthe 16 symptoms was compared among

three age groups (5-19, 20-64, 65+), reported symptoms did not

always increase with age. For eight symptoms in the summer and

six symptoms in the winter, highest prevalence rates were found

among the people between the age of 20 and 64 years.

Age, gender and smoking status are usually controlled in

epidemiologic studies as potential confounders to evaluate the

relationships between health effects and exposures. However, in

this study, the close association between the reported symptoms

and the presence of chronic respiratory/allergy conditions made

it neccessary that these conditions be controlled as well. The

strong association is indicated in Tables 2 and 3. Prevalence rates

of symptoms among the people with chronic diseases are higher

than those among females or smokers. Furthermore, all the differences between the people with and without chronic conditions

(except for the symptom ofnausea in the summer) are statistically

significant.

Due to the nonlinear relationship between age and symptoms,

the procedure of linear logistic regression was carried out on the

92
IRRITANTEFFECUS OFFORMALDEHYDE

Table 1. Characteristics of participants in the California HCHO study.

No. of participants (%)

Parameter Summer Winter

Gender

Male

Female

Age

4

5-19

20-64

2 65

Smoking

Yes

No

Respiratory/allergy conditions

Yes

No

Allergy

Yes

No

Asthma

Yes

No

Chronic bronchitis

Yes

No

Emphysema

Yes

No

Hayfever

Yes

No

Rashes

Yes

No

HCHO concentration

< 0.05 ppm

0.05-0.1 ppm

> 0.1 ppm

HCHO exposures, ppm-hr

< 7.0

7.0-12.0

> 12.0

645 (46.5)

743 (53.5)

46 (3.4)

135 (9.8)

739 (53.9)

452 (32.9)

372 (26.9)

1011 (73.1)

464 (33.3)

928 (66.7)

297 (21.3)

1095 (78.7)

59 (4.2)

1333 (95.8)

71 (5.1)

1321 (94.9)

42 (3.0)

1350 (97.0)

175 (12.6)

1217 (87.4)

86 (6.2)

1306 (93.8)

429 (30.8)

552 (39.7)

411 (29.5)

631 (46.7)

357 (26.4)

364 (26.9)

518 (47.4)

575 (52.6)

39 (3.6)

90 (8.3)

587 (54.0)

371 (34.1)

256 (23.4)

836 (76.6)

356 (33.5)

707 (66.5)

209 (19.7)

854 (80.3)

53 (5.0)

1010 (95.0)

77 (7.2)

986 (92.8)

34 (3.2)

1029 (96.8)

115 (10.8)

948 (89.2)

51 (4.8)

1012 (95.2)

220 (20.4)

535 (49.6)

323 (30.0)

406 (39.6)

337 (32.9)

282 (27.5)

Table 2. Percentage of participants with symptoms by gender, smoking

status, and respiratory/allergy diseases in summer phase.

Gender Smoker Respiratory/allergy

Symptom Female Male Yes No Yes No

Abdominal pain 7.0 2.8* 5.1 5.0 9.1 3.0*

Asthma attack 0.8 0.9 0.3 1.1 2.6 0.0*

Burning eyes 16.2 11.5* 17.0 13.0 25.9 8.1*

Burning skin 3.9 2.2 4.0 2.8 6.9 1.2*

Chest pain 5.8 3.1* 5.4 4.3 6.7 3.5*

Cough 19.8 14.3* 25.9 14.1* 28.5 11.5*

Diarrhea 9.7 6.5* 10.5 7.4 12.5 6.0*

Dizziness 8.1 4.0* 5.4 6.5 8.6 5.0*

Fatigue 15.2 11.2* 15.6 12.6 19.8 10.0*

Headache 26.2 14.9* 24.3 19.8 32.3 15.1*

Nausea 5.8 2.6* 4.3 4.4 5.6 3.7

Sleeping problems 19.4 12.7* 17.8 15.6 24.4 12.2*

Rashes 5.5 3.4 4.9 4.4 12.3 0.7*

Running nose 19.4 16.1 19.1 17.4 29.7 11.9*

Sore throat 11.7 7.1* 10.0 9.4 15.7 6.5*

Wheezing 8.1 7.0 11.3 6.2* 16.4 3.1*

*Significant result from x2 test with p-value less than 0.05.

age group with the largest sample size (age 20-64). In addition

to the independent variables ofgender, smoking status, chronic

respiratory/allergy diseases, and HCHOexposure, an interaction

Table 3. Percentage of participants with symptoms by gender, smoking

status, and respiratory/allergy diseases in winter phase.

Gender Smoker Respiratory/allergy

Symptom Female Male Yes No Yes No

Abdominal pain 4.5 2.0* 4.0 3.1 5.3 2.3*

Asthma attack 1.6 1.0 0.4 1.6 3.9 0.0*

Burning eyes 14.8 10.8 13.3 12.8 22.2 8.2*

Burning skin 2.5 2.2 3.2 2.1 3.7 1.7*

Chest pain 6.1 3.2* 7.2 4.0* 9.0 2.6*

Cough 24.6 21.2 31.7 20.2* 34.8 17.0*

Diarrhea 6.4 3.4* 6.4 4.6 8.7 3.1 *

Dizziness 7.3 4.0* 5.2 5.9 8.4 4.4*

Fatigue 11.2 6.6* 14.1 7.5* 12.1 7.5*

Headache 25.5 14.4* 24.1 19.1 33.4 13.6*

Nausea 5.9 1.8* 3.2 4.1 7.6 2.1*

Sleeping problems 16.6 10.0* 12.9 13.4 21.1 9.6*

Rashes 3.4 5.0 4.4 4.1 9.3 1.6*

Running nose 22.5 20.6 24.1 20.7 30.6 17.0*

Sore throat 14.1 11.4 11.7 13.1 17.7 10.3*

Wheezing 7.8 6.4 11.2 5.9* 16.6 2.4*

*Significant result from x2 test with p-value less than 0.05.

term of HCHO exposure and chronic diseases was also included in the logistic model. The logistic model can be expressed as

the following function:

ln(P/(1-P)) = a + b1X1 + b2X2 + b3X3 + b4X4 + cX3X4

where P = the probability of having a given symptom; XI =

gender; X2 = smoking status; X3 = chronic respiratory/allergy

disease status; X4 = HCHO exposure; and X3X4 = chronic

disease x HCHO exposure.

The results of the logistic regression on 16 symptoms for both

seasons are shown in Table 4. As can be seen from this table,

complaints of burning/tearing eyes, stinging/burning skin,

fatigue, and sleeping problems in the summer and burning/tearing eyes, chest pain, dizziness, sleeping problems, and sore

throat in the winter were significantly associated with HCHO exposure after all the important potential confounders were controlled. HCHO acted sometimes independently and sometimes

jointly with chronic diseases (as an interaction term) to affect the

irritant effects. The fact that some interaction terms reached the

0.05 significance level indicates a high probability that there were

synergistic effects between HCHO exposure and chronic diseases.

Since burning/tearing eyes were associated with HCHO exposure for both seasons, an attempt was made to establish the

relationship between HCHO exposures and percentages of people with eye symptoms by dividing subjects into three ranges of

exposure. The exposure-response relationship is shown in Figure

1. For the three ranges of HCHO exposure, the percentage of

people with burning/tearing eyes in the summer increased from

13.3% (<7.0 ppm-hr) to 17.1% (7.0-12.0 ppm-hr) and then to

21.4% (>12.0 ppm-hr). In the winter, the increases are from 10.8

to 14.7% and then to 20.6%.

Discussion

Because this study was a random survey, which covered the

entire State ofCalifornia and included mobile homes ofall ages,

the average measured HCHO concentrations were expected to be

lower than those from surveys of homes where occupants

93
94 LIUETAL.

Table 4. Variables significantly related with health symptoms for the

participants between 20 and 64 years of age.'

Significant independent variables

Symptom Summer (n = 726) Winter (n = 544)

Abdominal pain Gender

Asthma attack -

Burning eyes Gender, HCHO, chronic HCHO, chronic

Burning skin HCHO, smoker, chronic -

Chest pain Gender HCHO, smoker, chronic

Cough Smoker Smoker, chronic

Diarrhea

Dizziness Gender Gender, HCHO

Fatigue HCHO*chronicb Smoker

Headache Gender Gender

Nausea Gender Gender

Sleeping problems Gender, HCHO*chronicb Gender, HCHO

Rashes Chronic

Running nose Chronic

Sore throat Gender, chronic HCHO*chronic

Wheezing Smoker, chronic Smoker

aThe variables listed in this table are those entered into the linear logistic

regression function with p-values less than 0.05.

bHCHO*chronic indicates an interaction between these two variables.

25

---0 Summer -+I Wlnter

20

p

e

r

C

e

n

t

a 10

g

e

5

0

0-7.0 7.0-12.0 >12.0

HCHO Exposure (ppm x hrs)

FIGURE 1. Percentage of participants between 20 and 64 years having burning/tearing eyes by three ranges of HCHO exposures.

complained of symptoms. For these noncomplaint participants

chronically exposed to relatively low levels of HCHO, positive

associations were foundbetweenweek-longaverageHCHOexposures and irritant effects. Both in the winter phase and summer

phase, several irritant symptoms were relatedto HCHOexposures

when the potential confounders ofage, gender, smoking status,

and status ofchronic respiratory/allergy problems werecontrolled.

This indicates that HCHO-related irritant symptoms exist among

residents ofmobilehomes whohave not formally complained to

government agencies, suggesting that effects occur at lower

HCHO levels than previously thought.

Another significant finding ofthis study was the synergistic effect between HCHO exposure and chronic respiratory/allergy

problems. For persons with such chronic health problems, the

prevalence rates ofirritant symptoms were generally higher than

for those without chronic problems. Further, for some symptoms,

these rates wereeven higher than wouldbe expected ifthe effects of

HCHOexposure and chronic health problem were only additive.

Apositive exposure-response association was observed in this

study for burning/tearing eyes over the exposure ranges studied.

Further, responses were found at exposure levels as low as 7

ppm-hr. For a person who spends 60% of the time inside his or

her own home, a weekly HCHO exposure of 7 ppm-hr can be

translated into a weekly average HCHO concentration of 0.07

ppm. It is not uncommon to find HCHO concentrations at this

level in mobile homes (14). The fact that approximately 10,000

mobile homes are sold annually in California alone implies that

the affected population may be substantial.

Technical and administrative support for this study provided by B. Chang, G. Kulasingam, E. Kothny, M. Petreas, L. Pierce, and L. Webber is greatly appreciated.

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