airborne contact dermatitis ( abcd ) is a morphological diagnosis that encompasses all acute or chronic dermatoses predominantly of exposed parts of body , which are caused by substances which when released into the air , settle on the exposed skin . although the diagnosis of abcd is not difficult for the trained eye , finding the causative contactant and the treatment of the resultant clinical condition may prove to be a challenge for the treating dermatologist . airborne  on the basis of the history of the patient and the follow - up , existence of dust or of volatile causative agents , the morphology and distribution of the lesions and the results of epicutaneous tests . over the years , there has been an increasing recognition on the part of dermatologists regarding the occupational as well as the non - occupational airborne allergens and irritants . the present review is aimed at discussing the various epidemiological aspects of abcd , the newly observed occupational and non - occupational airborne contactants , the protean clinical manifestations and the therapeutic modalities available in abcd . this is primarily because of the fact that it can be very difficult and cumbersome to prove an abcd , especially of irritant type , and secondly because the term airborne has been less often used in literature . it is generally believed that occupational airborne irritant contact dermatitis is grossly underreported and is much more common compared to airborne allergic contact dermatitis . although abcd has been reported to be caused by a number of agents , most of which have been published as case reports or small case series , majority of the data from india and outside focus largely on plant antigens as being an important cause of abcd . cabanillas et al . , reported a 3% prevalence of allergic dermatitis to plant antigens among patients presenting with contact dermatitis in the allergy unit , mostly in abcd pattern . many authors have reported a significantly lower incidence and severity of sesquiterpene lactone ( sl ) sensitivity in east asian population ( 1.4% ) compared to european population ( 0.95.9%).[35 ] mak et al . , postulated that consumption of chrysanthemum since childhood in east asia may result in induction of oral tolerance . among the patients with sl sensitivity , one third acquire it occupationally . in india , parthenium dermatitis , caused by parthenium hysterophorus , it belongs to the family compositae , subfamily asteroide ( tribe heliantheae ) , which itself is a large , diverse group of the plant kingdom . it is a wind pollinated plant and produces an enormous quantity of pollen ( up to 624 million per plant ) that can be carried away in clusters of 600800 grains . lonkar and jog were the first to report the epidemic of parthenium dermatitis in agriculturists and field workers at pune , maharashtra , in 1968 . presently , it is the commonest cause of plant dermatitis in india and is responsible for 40% of patients attending contact dermatitis clinics . today , there is increased use of herbal ingredients in culinary , cosmetic and medicinal products . other members of the compositae family which are in wide use are the ornamental annuals like sunflowers , cosmos , marigold , asters ; herbaceous perennials like dahlia , chrysanthemum , marguerites ; vegetables like lettuce , chicory , artichokes ; herbal medicines like feverfew ( tanacetrim parthenium ) , pot marigold ( calendula ) ; natural insecticides like pyrethrum and weeds like bindii ( soliva pterosperma ) , ragweed , fleabane , stinkwort and capeweed . in a study by agarwal et al . , from south india , 50 patients with a clinical picture and history consistent with parthenium dermatitis due to exposure to p. hysterophorus were studied . the most common type of dermatitis was the classic abcd pattern ( 46% ) followed by the mixed pattern ( 30% ) , erythroderma ( 14% ) and chronic actinic dermatitis ( cad ) ( 10% ) . of the 40 patients patch tested , 90% had patch - test results positive for parthenium . in another study from delhi , 75 patients with clinically suspected contact dermatitis were patch tested with the indian standard series and indigenous antigens . parthenium was the most common contact sensitizer ( 20% ) , followed by potassium dichromate ( 16% ) , xanthium ( 13.3% ) , nickel sulfate ( 12% ) , chrysanthemum ( 8% ) , mercaptobenzothiazole and garlic ( 6.7% each ) . a study targeting regional danish floristry gardeners and greenhouse workers determined a lifetime prevalence of almost 20% of occupational dermatitis and identified working with compositae plants , having occupational mucosal symptoms or having a history of previous occupational eczema as the risk factors for developing occupational abcd . in airborne allergic dermatitis , initially there is a refractory phase where there is a periodic or continuous contact with allergen but no response . this is followed by an induction phase where the hapten penetrates skin , conjugates with epidermal protein , comes in contact with antigen presenting cells , migrates to draining lymph nodes followed by stimulation of naive t cells . this leads to proliferation of activated t cells to produce effector and memory cells which then enter the circulation . re - exposure to the specific hapten leads to the release of mediators producing skin inflammation . the inflammation may resolve with cellular and enzymatic degradation of antigen , inhibition of antigen presenting cells and stimulation of suppressor t cells . akhtar et al . , studied the cytokine profile in 50 patients with parthenium dermatitis , with all of them showing increased levels of pro - inflammatory cytokines like interleukin ( il)-6 , il-8 , il-17 and tumor necrosis factor ( tnf)- , and decreased levels of anti - inflammatory cytokines like il-4 and il-10 . a study investigating the relationship between polymorphisms of tnf and contact allergy found that the distribution of tnf-308 genotypes was significantly different between cases with contact allergy and healthy controls , with carriers of the a allele being more frequent among polysensitized patients . experimentally proved that dermatitis can be caused by inhalation of allergen with interplay of type 1 and 3 hypersensitivity . their patient showed a positive patch test to parthenium , positive delayed reaction to prick test on day 1 and histopathology showing vasculitis . in contrast , lakshmi et al . incriminated type 1 and 4 hypersensitivity in causation of abcd due to presence of positive prick test and raised serum ige levels in patients with patch test positive parthenium dermatitis . abcd to cedar pollen is a recently identified disease that generally affects individuals with nasal and/or ocular symptoms , as well as some patients with atopic dermatitis . it was suggested that in cedar pollinosis , pgd2-crth2 signaling contributes to inflammation , with the lesional skin showing il-13 , il-18 , eotaxin / chemokine ( c - c motif ) ligand ( ccl ) 11 , rantes / ccl5 , macrophage - derived chemokine / ccl22 and thymus and activation - regulated chemokine / ccl17 . fillagrin mutation , as in atopic dermatitis , has been linked to causation in contact dermatitis . however , studies so far have shown conflicting results . recently , poltromeri et al . gave the concept of occupational allergic march to describe the rapid evolution of contact dermatitis to ammonium persulfate into abcd with rhinitis and asthma in a hairdresser . inhalation of pollens , dusts , and animal hair causes either flare - up of atopic dermatitis or an apparent superimposed contact dermatitis ; in some instances , the airborne allergens may produce positive patch - test reactions ( i.e. with dermatophagoides ) . the common allergens and irritants which have been demonstrated to produce an airborne dermatitis like picture are listed in table 1.[12032 ] these include various acids and alkalis , metals and powders of metallic salts , cement , industrial solvents , glass fibers , sewage sludge , ammonia , vegetable and wood allergens , plastics , rubbers and glues , insecticides , pesticides , animal feed additives and many others . the airborne contactants can also be classified on the basis of their physical state as volatile airborne contactants like acids , alkalis , ammonia and pesticides ; droplets like insecticides , perfumes and hair sprays ; powders which include aluminum , anhydrous calcium silicate , and metallic oxides ; and particles like tree sawing particles , wool and plastics . common and newer antigens which can cause airborne contact dermatitis ( modified from santos et al . the most important allergens in p. hysterophorus responsible for allergic contact dermatitis are sls , consisting of a lactone ring combined with a sesquiterpene . parthenin , which belongs to the pseudoguinolide class of sls , is the major allergen . it has an alpha methylene group exocyclic to gamma lactone , which is probably essential for the induction of allergy . the other allergens that have similar group are coronopilin and tetraneurin a. the other components , namely , thiopenes , monoterpenes and acetylenes , are known to cause phytophotodermatitis . sls are also found in other genera , namely , liverwort ( frullania ) , tulip tree ( liriodendron , magnoliacea ) and sweetbay ( lauraceae , laurus nobilis ) . a person can be sensitised to airborne contactants by direct and indirect contact , ingestion of allergens in herbal teas or exposure to herbal cosmetics . dooms - goossens classified airborne dermatitis into five different types , namely , airborne irritant contact dermatitis , airborne allergic contact dermatitis , airborne phototoxic reactions , airborne photoallergic reactions and airborne contact urticaria . rare presentations include acne like , lichenoid eruptions , fixed drug eruptions , exfoliative dermatitis , telengiectases , paresthesias , purpura , erythema multiforme like eruption , pellagra like dermatitis and lymphomatoid cd . similarly , formaldehyde and phosphorus sesquisulfide can lead to an airborne irritant or allergic cd and contact urticaria . in the classical airborne allergic contact dermatitis , there is involvement of exposed areas of face ,  v  of neck , hands and forearms ,  wilkinson 's triangle ,  both eyelids , nasolabial folds and under the chin . the involvement of both light - exposed and protected areas helps to differentiate abcd from a photo - related dermatitis . another close differential is atopic eczema as both abcd and atopic eczema have predominant flexural and skin crease involvement . initially , there is an acute flare of the dermatitis during the plant growing season but , with repeated exposure , the flare becomes prolonged and produces a chronic lichenified eczema associated with secondary infection , fissuring and hypo or hyperpigmentation . in patients wearing glasses , dermatitis occurs at the edge of nose due to occlusion . some patients present with facial swelling before manifesting classical eczematous lesions . verma et al . , put forward a clinical severity score ( css ) to assess the severity of abcd [ table 2 ] . it takes into consideration both the subjective features like pruritus experienced by the patient as well as the objective features like the morphology of lesions and the area involved . airborne agents like fibrous materials ( such as glass fibers , rock wool , and grain dust ) give rise to mechanical dermatitis by friction due to their abrasive physical properties . dust that contains glass fibers can produce cuts from sharp glass fragments , and asbestos  corns  may be seen on palmer aspect of fingers on exposure to spicules of asbestos . a lichenified dermatitis may be produced by wood and cement dust collecting around the collar , belt line , or sleeve end and other points of contact . clinical severity score to assess severity of abcd ( adapted from verma et al . ) alternatively , abcd can be subclassified into that of plant origin and non - plant origin . wood and plants are a rich source of airborne allergens and irritants , the causative agent often being the dried botanical material . the most commonly seen parthenium dermatitis classically presents as abcd but may occasionally present with photosensitive lichenoid eruption in morphology and distribution . a study observing the evolution of parthenium dermatitis recruited 74 patients who were classified into abcd , cad pattern or mixed pattern dermatitis . sixty patients had abcd , five had mixed pattern and nine had cad pattern at the onset . of the 60 patients with abcd , 27 changed to cad pattern and 11 to mixed pattern after an average period of 4.2 years . additionally , sawdust from teak , redwood , mahogany , and rosewood may contain sensitizers that produce a dry dermatitis , particularly on the face , penis , and scrotum in carpenters and woodworkers . dermatitis of woodworkers may be caused also by liverworts ( sls ) and lichens ( usnic acid or atranorin ) found on the bark of trees . cement dust usually presents as a dry , lichenified dermatitis due to its alkaline and hygroscopic properties . the eruption tends be dry rather than oozy even in cases of allergic contact dermatitis to the chromium or cobalt content in cement . genital dermatitis due to indirect hand contact and accumulation of sawdust on the clothes is often seen in cabinet makers . turpentine used to be the most frequent cause of airborne dermatitis , but is seen rarely now . polyolefins , when heated , degrade and form aldehydes , ketones , and acids and very rarely induce airborne dermatitis . additionally , plastic , rubber , glues , metals , insecticides , pesticides , solvents , and other industrial and pharmaceutical chemicals have been described as causing airborne dermatitis . while managing abcd , care must be taken to distinguish between occupational and non - occupational disease and between irritant and allergic occupational abcd , as management will differ . a temporal correlation with work only raises the suspicion which needs to be confirmed with patch test or prick test . in suspected cases of occupational irritant dermatitis , the responsible agent may be isolated by means of chemical analysis or direct microscopic study of the air or material in the air . photopatch tests can be useful for excluding light as a factor in the pathogenesis of the lesions . during patch testing , volatile allergens sometimes also cause irritant dermatitis ; therefore , high dilutions should be used . sometimes special glass cups which permit exposure to the vapor of allergen have to be used . for testing wood dust sl mix 0.1% petrolatum is commercially available and consists of equimolar quantities of three pure sls ( alantolactone , dehydrocostus lactone and costunolide ) . in a study , only 35% of cases of compositae allergy were detected by using only sl mix and it was concluded that sl mix was not an adequate screening test . these patients can be identified by using additional compositae extracts like dandelion or feverfew extracts when there is a clinical suspicion of compositae allergy . another study comparing compositae mix with sl mix was done in which compositae mix led to few irritant reactions and less false - negative test results as compared to sl mix . it was concluded that compositae dermatitis is being underdiagnosed and that the compositae mix is significantly more sensitive in detecting compositae allergy than the sl mix . severity of contact dermatitis depends upon degree of contact hypersensitivity and quantity of antigen to which the patient is exposed . for effective control of dermatitis as the hypersensitivity is difficult to be reduced , the only option is to reduce quantity of antigen to which patient is exposed . substitution reduces the incidence of occupational dermatitis and urticaria . in cases of abcd due to parthenium , one should avoid going outdoors on days when pollen are present in high concentrations in air , especially in summers and in the months from september to november following the north - east monsoon showers . simple routines like taking a bath after coming indoors ; wearing fresh clothes and eliminating weeds and grasses in the house garden can offer great help . use of a barrier cream on the exposed areas after every wash is important to slow down penetration of antigen into skin . other measures which can be used are photoprotection , sunscreens , change of job , change of residence , antihistamines , drying agents in cases of weeping eruptions , aluminum sulfate and calcium acetate and emollients for lichenified areas , etc . they decrease the number of hla dr+ langerhans cells and inhibit the production and function of il-1 , il-2 and interferon ( ifn)-. systemic steroids decrease t cell proliferation and are indicated when there is more than 25% body surface area involvement and when dermatitis is suspected to be caused by allergens which persist in the skin for weeks after exposure ( toxicodendron oleoresins ) . psoralens and uva ( puva ) decreases hla dr+ langerhans cells [ lc ] , whereas uvb induces epidermal hyperplasia and pge . it blocks dna replication by incorporating 6-thioguanine into dna and prevents lymphocytic proliferation after antigenic stimulation . both the number and antigen presenting capacity of lc are affected . in a study , the response was excellent ( 80100% clearance of disease ) in 58.3% patients and good ( 60% clearance ) in 41.7% patients . the cost of therapy with this regimen was reduced by 60% . in another therapeutic study on patients of parthenium dermatitis , three therapeutic regimens with azathioprine were used . a total of 22 patients ( group i ) were given 50 mg azathioprine twice a day , 11 patients ( group ii ) received 50 mg azathioprine per day and 300 mg azathioprine every 28 days , and 10 patients ( group iii ) were given 50 mg azathioprine twice a day along with 300 mg azathioprine every 28 days . twenty out of 22 in group i and 9/11 patients in group ii and 9/10 patients in group iii had complete remission . nine out of 22 , 7/11 and 6/10 patients in the respective groups needed additional oral betamethasone 12 mg per day for brief periods only during the peak season in order to maintain complete remission . sharma et al . , treated 16 patients with parthenium dermatitis , unresponsive to topical treatment , with oral methotrexate ( 15 mg / week ) . seven patients completed 6 months or more of follow - up , and their mean dasi fell to 5 , 2.7 and 2.1 at the end of 1 , 3 and 6 months , respectively , from a baseline score of 10 . hyposensitization refers to introduction of an antigen into the body by a route different from the natural one , to induce such a change in the immune system that the body does not develop clinical manifestations when the antigen is introduced into the body through normal route . oral hyposensitization , although demonstrated to be effective for ragweed dermatitis , has not been widely accepted because it carries considerable risk of provoking and worsening eczema . in some cases , patients are co - sensitized with several unrelated pollen allergens . based on frequent co - sensitization patterns , some of the hybrid proteins have been developed with the polymerase chain reaction . antibodies induced with the hybrids in mice inhibited the binding of grass pollen - allergic patients immunoglobulin e to each of the individual allergens and grass pollen extract , and may thus represent protective antibodies . handa et al . , evaluated the effect of oral hyposensitization as an alternative therapeutic modality and observed a gradual improvement in the clinical status of 70% of those patients who completed the study , as evident from a fall in their clinical severity score for eczema . the treatment had to be stopped in 30% of patients as they experienced an exacerbation during the course of the study . overall , patients tolerated the therapy well and no significant side effects were seen , except for abdominal pain ,  heartburn  and cheilitis . evidence indicates that up to 50% of patients with abcd , whether occupational or non - occupational , experience adverse effects on quality of life , daily function and personal relationship , and take time off work on sick leave and may lose or change job because of their skin disease . a significant proportion of patients still tend to have active symptoms many years after diagnosis , despite treatment and change of job . however , it should be emphasized to all that avoidance of further exposure can lead to recovery from dermatitis in many cases . with respect to abcd occurring secondary to parthenium dermatitis , there are continuing attempts to control the spread of the weed through biological measures like introduction of exotic arthropods and opportunistic pathogens , use of antagonistic plants and bioherbicides as well as use of selective chemical herbicides .