Allergic contact dermatitis skin penetration

Allergic contact dermatitis is a delayed hypersensitivity reaction.30 Upon initial exposure, a substance penetrates the skin, binds to a protein and develops into sensitizing antigens. Subsequent exposures to that substance will then elicit an allergic reaction.25,29,30 Symptoms of allergic contact dermatitis are similar to those of the irritant type, but may take several hours to several days to develop following re-exposure.25,26... 

The interaction of a chemical (hapten) with epidermal proteins (carrier) can result in a hapten-carrier complex capable of activating skin-associated lymphoid tissue (sensitisation) and dissemination of antigen-specific T l)unphocytes (induction). Subsequent encoimter with the same or cross-reactive chemicals can result in the elicitation of a characteristic inflammatory skin reaction. The clinical condition is referred to as allergic contact dermatitis and is characterised by erythema, oedema, vesiculation and pruritus. Allergic contact sensitisation is, therefore, classed as a cell-mediated immunological response to chemicals that contact and penetrate the skin. 

The substance may penetrate the skin and cause allergic contact dermatitis (formaldehyde, nickel, phthalic anhydride)... 

Urea, a physiological non-allergic substance [77, 84], has long been used in dermatological therapy. Urea can decrease reversibly the turnover of epidermal cells [41] and may also enhance the penetration of other substances into the skin [24, 77, 96]. Other effects include binding water in the horny layer, antipruritic, and reducing contact dermatitis from irritant stimuli [53> 77> 78, 84] ... 

Toxic solvents, such as methyl alcohol, benzene, and chlorinated hydrocarbons, can penetrate the skin through cuts and abrasions. On contact, these solvents cause chronic dermatitis and allergic skin reactions in susceptible individuals. 

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