Allergic Contact Dermatitis (Skin Allergies)
History: A detailed history, both before and after patch testing, is crucial in evaluating individuals with ACD. Potential causes of ACD and the materials to which individuals are exposed should be patch tested. Patients with ACD require a much more detailed history compared to those with most other dermatologic disorders.
History is equally important after patch testing. Only history and questioning can determine whether the materials to which a patient is allergic are partly or wholly responsible for the current dermatitis. A positive patch reaction may indicate only a sensitivity and not the cause of current dermatitis.
- Preexisting skin diseases
- Individuals with stasis dermatitis are at high risk for developing ACD to materials and agents applied to the areas of stasis dermatitis and leg ulcers. Neomycin is an important cause of ACD in these individuals because it is used frequently despite the lack of documentation of its efficacy in the treatment of stasis ulcers.
- Individuals with otitis externa frequently are allergic to topical neomycin and topical corticosteroids.
- Individuals with pruritus ani and pruritus vulvae may become sensitized to benzocaine and other medications applied to chronic pruritic processes.
- Women with lichen sclerosus et atrophicus frequently develop ACD, complicating the severe chronic vulvar dermatosis. Patch testing these patients may provide important information that can help in the management of recalcitrant and difficult-to-manage dermatosis.
- Atopic dermatitis
- Patients with a history of atopic dermatitis are at increased risk for developing nonspecific hand dermatitis and irritant contact dermatitis.
- Patients with a history of atopic dermatitis do not appear to be at an increased risk for ACD, despite the wide range of topical medications and moisturizers used by individuals with chronic atopic dermatitis.
- Patients with atopic dermatitis are at lower risk of ACD to poison ivy.
- Some European studies indicate that patients with atopic dermatitis may have increased incidence of ACD to nickel.
- Individuals with ACD typically develop dermatitis (within a few days of exposure) in areas that were exposed directly to the allergen. Certain allergens (eg, neomycin) penetrate intact skin poorly, and the onset of dermatitis may be delayed up to a week following exposure.
- A minimum of 10 days is required for individuals to develop specific sensitivity to a new contactant.
- An individual who never has been sensitized to poison ivy may develop only a mild dermatitis 2 weeks following the initial exposure but typically develops severe dermatitis within 1-2 days of the second and subsequent exposures. Remember that removing the poison ivy allergen from the skin is difficult, and unless an individual washes exposed skin within 30 minutes of exposure, ACD will develop. The hallmark of the diagnosis of poison ivy is linear dermatitic lesions.
- The possibility of an external cause of dermatitis always must be considered if the dermatitis is linear or sharply defined. The immediate onset of dermatitis following initial exposure to material suggests either a cross-sensitization reaction, prior forgotten exposure to the substance, or nonspecific irritant contact dermatitis provoked by the agent in question.
- Eyelid dermatitis: Individuals may develop dermatitis on eyelids and other exposed skin following exposure to airborne allergens.
- Immediate reactions, ie, visible lesions developing less than 30 minutes after exposure, indicate contact urticaria (not ACD), particularly if urticarial in appearance and if associated with other symptoms such as distant urticaria, wheezing, ophthalmedema, rhinorrhea, or anaphylaxis.
- Rubber latex currently is the most important source of allergic contact urticaria (see Latex Allergy). The term hypoallergenic may refer to gloves that do not contain sensitizing chemicals added to rubber latex but may not indicate whether the gloves are rubber latex free. Some individuals may have delayed specific contact sensitivity to rubber latex, but contact urticaria to rubber latex is much more common than ACD to latex. Individuals with hand dermatitis, hospital workers, children with spina bifida, and atopic individuals are at increased risk of developing contact urticaria to rubber latex. Individuals may have ACD to chemicals added to rubber gloves and have contact urticaria to latex. Individuals wearing rubber gloves should be evaluated carefully for both possibilities.
- Rare reports exist of immediate anaphylactic reactions to topical antibiotics (eg, bacitracin).
- Occupational dermatitis: Contact dermatitis is 1 of the 10 leading occupational illnesses. It may prevent individuals from working. The hands are the sites exposed most intensely to contact allergens and irritants, both at work and at home. The hands are crucial for performing many work-related tasks. ACD in response to workplace materials may improve initially on weekends and during holidays, but individuals with chronic dermatitis may not demonstrate the classic history of weekend and holiday improvement. Irritant contact dermatitis is more likely if multiple workers are affected in the workplace. Most allergens rarely sensitize a high percentage of the population.
- Hobbies: Hobbies may be the source of ACD, eg, woodworking with exotic tropical woods or processing film using color-developing chemicals that may provoke cutaneous lesions of lichen planus from direct skin exposure.
- Medications: Self-prescribed and physician-prescribed medications are important causes of ACD. The workplace nurse may dispense ineffective and sensitizing topical preparations, such as Merthiolate, which may change a simple abrasion into a severe case of ACD. Individuals may develop allergy to preservatives in medications and/or to the active ingredients in topical medications, especially neomycin and topical corticosteroids.
- Iatrogenic adverse effects: Chronic use of systemic corticosteroids to treat ACD may produce severe morbidity. Individuals with ACD should not receive chronic systemic corticosteroids or immunosuppressives, unless extensive patch testing and evaluation have failed to identify remedial causes of the severe dermatitis. Chronic widespread use of potent topical corticosteroids may produce local skin atrophy and systemic adverse effects.