Allergic contact dermatitis hypersensitivity

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... 

Topical Hypersensitivity reaction (allergic contact dermatitis, burning, inflammation, pruritus)... 

CN may cause primary irritant dermatitis or allergic contact dermatitis by delayed hypersensitivity. After sensitization, acute exposure to CN causes itching, erythema, edema, vesiculation, purpura, and necrosis.28 Jolly and Carpenter reported that an accidental discharge of a pen gun resulted in erythema and edema 24 h later the patient had been exposed to CN 5 yr earlier. Queen and Stander reported severe reactions to CN 17 yr after a first exposure to the agent. 

Plasma levels of doxepin similar to those achieved during oral therapy may be obtained with topical application the usual drug interactions associated with tricyclic antidepressants may occur. Therefore, monoamine oxidase inhibitors must be discontinued at least 2 weeks prior to the initiation of doxepin cream. Topical application of the cream should be performed four times daily for up to 8 days of therapy. The safety and efficacy of chronic dosing has not been established. Adverse local effects include marked burning and stinging of the treatment site which may necessitate discontinuation of the cream in some patients. Allergic contact dermatitis appears to be frequent, and patients should be monitored for symptoms of hypersensitivity. 

Allergic contact dermatitis from transdermal estrogen has been described in Korea, where the reaction was found to be due to 17-P-estradiol itself and not to an excipient (226). In some cases, allergic reactions and systemic contact dermatitis are clearly attributable to the patch material or to excipients. Even natural estradiol given in this way can occasionally cause hypersensitivity reactions, as determined by patch tests (227). 

Xenobiotics can affect allergic disease in one of two ways. They can themselves act as antigens and elicit hypersensitivity responses, or they can enhance the development or expression of allergic responses to commonly encountered allergens, such as dust mite. Chemicals that act as allergens include certain proteins that can by themselves induce an immune response and low molecular weight chemicals (known as haptens) that are too small to induce a specific immune response but may react with a protein to induce an immune response that is then hapten specific. Haptens have been associated with both allergic contact dermatitis (ACD), sometimes called contact hypersensitivity... 

The allergic variety of contact dermatitis is a type IV hypersensitivity response involving sensitization of T lymphocytes. Antigens form after the sensitizing substance (haptens or partial antigens) comes into contact with the dermal protein fc>r the first time, which results in sensitization. Sensitization may take weeks to years to develop. On reexposure to the same or a related substance, a delayed inflammatory response is elicited, usually within 48 to 72 hours. Allergic contact dermatitis is often associated with the eyelids or periocular area and in some instances may involve the face and the hands. 

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