the interaction of ultraviolet or visible light of a specific wavelength with certain molecules or photosensitizing chemicals leads to a delayed type hypersensitivity reaction that causes photocontact dermatitis . the primary investigation for the detection of photodermatitis is the photopatch test , which helps in the investigation and detection of specific allergens that cause photodermatitis in a susceptible individual . it involves exposure of the skin to appropriate amounts of an allergen implicated in causing photoallergic contact dermatitis and recording the subsequent response with and without light exposure . the primary indication for the test would be dermatitis predominantly limited to sun exposed sites of uncertain aetiology . the antigens used in the photopatch series include sunscreens , nonsteroidal anti - inflammatory drugs ( nsaids ) , and fragrances ; specific antigens are added based of information provided by the patient . although various differences exist in the procedure , irradiation doses , interpretation , and antigens of photopatch test , only 4%20% of patients undergoing photopatch tests show clinically positive relevant results . common photosensitizing agents include chemicals present in sunscreens , antiseptic agents , fragrances , and nonsteroidal anti - inflammatory drugs . in india , parthenium hysterophorus is probably the most common cause of photoallergic contact dermatitis and airborne contact dermatitis . the diagnosis of a photodermatitis is based on the history and clinical examination and is confirmed by photopatch testing . it is important to rule out other causes of photoexposed site reactions such as connective tissue disease , drugs , allergic contact dermatitis , and pophyrias while investigating a patient of suspected photoallergy . there is no indian standard photopatch test series available , and studies carried out in india have used european or scandinavian photopatch test trays , which may not be relevant for indian patients . hence we have used a combination of photopatch test and uv - irradiated indian standard series ( iss ) in our study , to detect light - induced antigens in patients with photosensitive dermatitis . this study was done as a hospital - based , descriptive , observer blinded study . a total of 35 patients were included in the study during a one year period between september 2012 and october 2013 . clearance from the ethical committee was obtained and written informed consent was taken from all patients involved in the study . patch and photopatch testing was performed on all the patients using the iss and photopatch series . 1- control , 2- potassium dichromate , 3- neomycin sulfate , 4- cobalt chloride , 5- benzocaine , 6- formaldehyde , 7- paraphenylenediamine ( ppd ) , 8- parabens , 9- nickel sulfate , 10- colophony , 11- gentamicin , 12- mercapto mix , 13- epoxy resin , 14- fragrance mix , 15- mercaptobenzothiazole , 16- nitrofurazone , 17- polyehyleneglycol-400 , 18- chlorocresol , 19- wool alcohols , 20- balsam peru , 21- thiruram mix , 22- chinoform , 23- black rubber mix , and 24- p - tbp f resin . the photopatch series consisted of : 1- benzophenone-3 , 2- benzophenone-4 , 3- eusolex 232 , 4- butylmethoxydibenzoyl methane ( parsol 1789 ) , 5- para amino benzoic acid , 6- 3(4 methyl benzyliden ) camphor , 7- octyltriazone , 8- octyl methoxycinnamate , 9- ibuprofen 5% , 10- piroxicam 5% , 11- ketoprofen 2.5% , 12- isomyl 4-methoxycinnamate 10% , 13- fragrance mix 8% , and 14- parthenium . the patients included in the study presented with dermatitis predominantly affecting sun exposed areas or with a history of photosensitivity . clinically suspected cases of phototoxic or photoallergic contact dermatitis secondary to drugs , chemicals , or airborne antigens were also included in the study . patients on systemic immunosuppressants , oral steroids , exfoliative and active dermatitis , pregnant or lactating women , and those below 18 years of age were excluded from the study . those with photosensitivity due to conditions such as connective tissue disease and genetic disorders with photosensitivity were also excluded . a detailed history was taken with regard to onset , duration and progression of disease , type and distribution of lesions , and presence of any comorbid conditions . all patients that fit the criteria for inclusion were subjected to a thorough clinical examination . photographs of the patch test sites were taken at each reading to document positive reactions . both sets of patches were applied in duplicate on the patient 's back , on either side of the spine by the standard method . after 24 h , the tapes were carefully removed and squares representing each chamber were marked using a marker pen . readings were recorded after a gap of half an hour , into the respective proformas . after noting relevant readings , one side was closed with an opaque black cloth and the other side was irradiated with 14 j / cmsq of uva . the selection of side to be irradiated was done in a randomized , observer - blinded manner . a distance of 15 cm was kept between the patient 's back and irradiation source . readings were then recorded after 48 h. at the end of the protocol , two sets of readings were obtained considering the day of patch application as day 0 . first reading was at 24 h after application of patches , followed by uva irradiation ( day 1 ) . the patch test results were evaluated using the international contact dermatitis research group ( icdrg ) grading . photopatch test was interpreted according to the standard photopatch criteria . according to the criteria , if only the irradiated side shows a positive reaction , it is labeled as a photoallergic reaction . if both sides show a positive reaction with the irradiated side showing greater than 1 + positivity , it is termed as a contact dermatitis with photoaggravation . if both sides show equal reaction after irradiation , a contact allergy is the result . out of the 35 patients included in the study , 10 ( 29% ) were females and 25 ( 71% ) were males and all patients were outdoor workers . majority ( 66% ) of patients belonged to the age group ranging from 35 to 65 years . a total of 24 ( 69% ) patients had positive patch or photopatch test results . majority of these patients 21 ( 60% ) had features of chronic dermatitis confined mainly to the sun - exposed areas with a history of photosensitivity . the remaining 14 ( 40% ) patients presented with a history of photosensitivity with dermatititis present both in sun - exposed and covered areas . twelve patients among the total study population had a positive history of atopy with ige levels above 1000 iu / ml . the highest number of photopatch reactions was noted with parthenium , with 18 ( 51% ) patients showing positive results . the detailed results of the 18 patients with a positive photopatch test suggestive of photodermatitis are shown in table 1 . out of the 18 patients , 9 ( 50% ) showed contact allergy , 4 ( 22% ) had photoallergy , and 5 ( 28% ) had contact dermatitis with photoaggravation to p. hysterophorus . five patients among the 18 patients had coexistent contact dermatitis to other antigens in the iss . detailed results of the 18 patients who showed positive photopatch test results six patients had contact dermatitis without any photoaggravation or photoallergy to varied antigens such as potassium dichromate , chinoform , fragrance , para - phenylenediamine , nickel , and cobalt . in our study , p. hysterophorus was the leading allergen with 51% of the study population showing a positive reaction . this is expected due to the widespread presence of parthenium in the locality and surrounding areas . in a similar study carried out by jindal et al . , 30 patients were subjected to photopatch testing along with some antigens obtained from the standard series . fourteen positive tests to several allergens were obtained with fragrance mix being the leading antigen ( 30% ) , followed by para - phenylenediamine ( 20% ) and p. hysterophorus ( 17% ) . sharma and kaur found 78% of patients with airborne contact dermatitis to have parthenium sensitivity . in another study done by sharma et al . three patients showed photoallergic reaction and another 3 showed photoaggravation out of 19 patients . in our study 4 patients showed photoallergy and 5 patients showed contact dermatitis with photoaggravation . the major antigens in p. hysterophorus are sesquiterpene lactones . some of the identified lactones are parthenin , hymenin , ambrosin , and coronopilin . parthenium is established to cause both photoallergy and contact dermatitis with photoaggravation . in a study done by kar et al . , it was observed that parthenium plays a significant role in the initiation and spread of air borne contact dermatitis and chronic actinic dermatitis ( cad ) . a 20-year analysis of antigens causing photoallergic contact dermatitis done in new york showed 11.6% positivity to plant derivatives including sesquiterpene lactone mix . the coexistence of allergic contact dermatitis ( acd ) with cad is well known . in most of these cases about 75% of patients with cad show a positive patch test response to one or more allergens . among the various plant antigens , sesquiterpene lactones obtained from plants of the compositae family are the most common causative antigens apart from fragrance , rubber , metals , colophony , chromates , and sunscreens . the second most common allergens in our study were fragrance mix and potassium dichromate . in our study , photoallergy due to fragrance can be due to the perfume compound itself of the fixative agent such as musk ambrette . in a study done by panja et al . , fragrance mix was the leading photosensitizer . metals such as nickel , cobalt , and dichromates are common sensitizing agents . three patients ( 30% ) showed positive patch test reactions , to nickel and cobalt in our study . these sensitizers are found in jewelry , watches , cement , leather , and dyes . chronic exposure to these allergens in the presence of ultraviolet radiation facilitates increased immune recognition and aggravation of pre - existing dermatitis . various differences exist in the pattern of antigen positivity depending on the area and population under study . the positivities obtained in western literature are to certain antigens not so frequently encountered in the indian scenario . in a recent study from the united states , sunscreens and anti - microbial agents were the predominant antigens and a decreased incidence in fragrance induced photoallergic contact dermatitis was found . the most common positive antigens in photopatch tests in western studies were sunscreens and drugs such as nsaids . no positivity to sunscreens was detected in our study , probably due to infrequent use in the given population . the leading allergens in the scandinavian multicentric photopatch study were musk ambrette and para amino benzoic acid . one patient showed positive reaction to ppd . in a study done by jindal et al . 6 out of 20 patients showed contact allergy to ppd with two patients having photoaggravation . although ppd is known to cause photoallergic reactions , our patient did not exhibit the same . in our study , six patients had contact dermatitis to various antigens such as nickel , cobalt dichromates , and ppd . although these sensitizers have been implicated in photoaggravated contact dermatitis , none of our patients showed such a response pattern . photodermatitis is prevalent in india , and prompt identification of the causative antigens will alleviate the morbidity associated with this condition . photoallergic contact dermatitis is largely underdiagnosed in our country due to lack of availability of proper photopatch protocols . parthenium was found to be the leading cause of photodermatitis in our study causing photoallergy , contact dermatitis with photoaggravation , and contact allergy . among the 18 parthenium - positive patients , five had coexistent contact dermatitis to other antigens in the iss . in this context , patch testing with both iss and photopatch series could lead to clinically relevant results . it is advantageous as it is noninvasive , simple to carry out , and can be performed on an outpatient basis . thus , patch testing with combined iss and photopatch series can be efficacious in the detection of antigens causing photosensitive dermatitis . 
 a 24- and 48-h photopatch test reading was taken . our inability to take delayed readings at 72/96 h or even one week may have resulted in false - negative results.minimal erythema dose or med is the least amount of uv radiation required to produce perceptible erythema on light exposed skin . 48-h photopatch test reading was taken . our inability to take delayed readings at 72/96 h or even one week minimal erythema dose or med is the least amount of uv radiation required to produce perceptible erythema on light exposed skin . a 24- and 48-h photopatch test reading was taken . our inability to take delayed readings at 72/96 h or even one week may have resulted in false - negative results.minimal erythema dose or med is the least amount of uv radiation required to produce perceptible erythema on light exposed skin . 48-h photopatch test reading was taken . our inability to take delayed readings at 72/96 h or even one week minimal erythema dose or med is the least amount of uv radiation required to produce perceptible erythema on light exposed skin .
background : the photopatch test is used to detect photoallergic reactions to various antigens such as sunscreens and drugs . 
 photosensitive dermatitis can be caused due to antigens like parthenium , fragrances , rubbers and metals . 
 the photopatch test does not contain these antigens . 
 therefore , the indian standard series ( iss ) along with the standard photopatch series from chemotechnique diagnostics , sweden was used to detect light induced antigens.aim:to detect light induced antigens in patients with photosensitive dermatitis.methods:this study was done in a descriptive , observer blinded manner . 
 photopatch test and iss were applied in duplicate on the patient 's back by the standard method . 
 after 24 hours , readings were recorded according to icdrg criteria . 
 one side was closed and other side irradiated with 14 j / cm2 of uva and a second set of readings were recorded after 48 hrs.result:the highest positivity was obtained with parthenium , with 18 out of 35 ( 51% ) patients showing a positive patch test reaction with both photoallergic contact dermatitis and photoaggravation . 
 four patients ( 11% ) showed positive patch test reaction suggestive of contact dermatitis to potassium dichromate and fragrance mix . 
 six patients had contact dermatitis to numerous antigens such as nickel , cobalt , chinoform and para - phenylenediamine . 
 none of these patients showed photoaggravation on patch testing.conclusion:parthenium was found to cause photoallergy , contact dermatitis with photoaggravation and contact allergy . 
 hence , photopatch test and uv irradiated patch test can be an important tool to detect light induced antigens in patients with photosensitive dermatitis .