p-Phenylenediamine (PPD) - although its mainly used as a component of engineering polymers and composites like kevlar, it is also an ingredient in hair dyes which once sensitized to, becomes lifelong. One can develop active sensitization to products, including but not limited to black clothing, various inks, hair dye, dyed fur, dyed leather, and certain photographic products. Photographic developers, especially those containing metol
Quaternium-15 – preservative in cosmetic products (self-tanners, shampoo, nail polish, sunscreen) and in industrial products (polishes, paints and waxes). Sap from certain species of mangrove and agave
Soluble salts of platinum – see platinosis
Thiomersal – mercury compound used in local antiseptics and in vaccines
Topical anesthetics – such as pramoxine or diphenhydramine, after prolonged use
Topical steroid – see steroid allergy
Urushiol – oily coating from plants of Toxicodendron genus –  poison ivy, poison oak, and poison sumac. Also found in mango plants, mango skin, cashews, and smoke from burning urushiol-containing plants, which can cause skin as well as severe lung irritation. Mechanism
ACD arises as a result of two essential stages: an induction phase, which primes and sensitizes the immune system for an allergic response, and an elicitation phase, in which this response is triggered. As it involves a cell-mediated allergic response, ACD is termed a Type IV delayed hypersensitivity reaction, making it an exception in the usage of the designation "allergic," which otherwise usually refers to type I hypersensitivity reactions.
Commonly, the symptoms may resolve without treatment in 2 to 4 weeks but specific medication may hasten the healing as long as the trigger is avoided. Also, the condition might become chronic if the allergen is not detected and avoided. Identification of the allergen can be aided by the site of the dermatitis. Allergic dermatitis of the hands is often due to contact with preservatives, fragrances, metals, rubber, or topical antibiotics. Dermatitis at the front of the face is often due to gold (from jewelry and foundation), make-up, moisturizers, wrinkle creams, and topical medication. Along the eyelids as well as the sides of the head and neck, dermatitis is often caused by shampoo and conditioner dripping down from the hair. Inflammation on one side of the face often suggests transfer of an allergen from the hands or from the face of a partner. Epidemiology
Allergic contact dermatitis is common, affecting up to 20% of all people. People sensitive to one allergen are at an increased risk of being sensitive to others. Family members of those with allergic contact dermatitis are at higher risk of developing it themselves. Women are at higher risk of developing allergic contact dermatitis than men. References


== External links ==