History
A detailed history, both before and after patch testing, is crucial in evaluating individuals with allergic contact dermatitis. Potential causes of allergic contact dermatitis and the materials to which individuals are exposed should be included in patch testing. Evaluation of allergic contact dermatitis requires a much more detailed history than most other dermatologic disorders.
Awareness of current trends is also important. The increased use of face masks in the coronavirus disease 2019 (COVID-19) pandemic has been associated with contact dermatitis due to formaldehyde releasers. [17]
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 allergic contact dermatitis to materials and agents applied to the areas of stasis dermatitis and leg ulcers. Neomycin and bacitracin are important causes of allergic contact dermatitis in these individuals because they are used frequently despite the lack of documentation of their 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 allergic contact dermatitis, 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. They are at lower risk of allergic contact dermatitis to poison ivy. An inverse association was found between contact sensitization and severe atopic dermatitis. Inverse associations were found for all groups of allergenic chemicals and metals, except for sensitization to fragrances and topical drugs, for which positive associations were identified.
Onset of symptoms
Individuals with allergic contact dermatitis 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. For example, 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, allergic contact dermatitis 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 or allergens transferred to that site by the fingers. Contact dermatitis may also result from allergy to eyelid makeup.
Contact urticaria
Immediate reactions, ie, visible lesions developing less than 30 minutes after exposure, indicate contact urticaria (not allergic contact dermatitis). This is particularly true if the lesions are urticarial in appearance and if the skin reaction is associated with other symptoms, such as distant urticaria, wheezing, ophthalmedema, rhinorrhea, or anaphylaxis.
Latex
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 allergic contact dermatitis 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 allergic contact dermatitis 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. Allergic contact dermatitis 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 allergic contact dermatitis. Examples include 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
Medications (both self-prescribed and physician-prescribed) are important causes of allergic contact dermatitis. The workplace nurse may dispense ineffective and sensitizing topical preparations, such as thimerosal (Merthiolate), which may change a simple abrasion into a severe case of allergic contact dermatitis. Individuals may develop allergy to preservatives in medications and/or to the active ingredients in topical medications, especially neomycin and topical corticosteroids. [18, 19]
Patients with dermatitis that does not clear with topical corticosteroid treatment should be considered for patch testing with a corticosteroid series and the commercial preparations of corticosteroids and their vehicles.
Physical Examination
Acute allergic contact dermatitis is characterized by pruritic papules and vesicles on an erythematous base. Lichenified pruritic plaques may indicate chronic allergic contact dermatitis. Occasionally, allergic contact dermatitis may affect the entire integument (ie, erythroderma, exfoliative dermatitis). The initial site of dermatitis often provides the best clue regarding the potential cause of allergic contact dermatitis. Note the following.
Hands
Hands are an important site of allergic contact dermatitis, particularly in the workplace. Common causes of allergic dermatitis on the hands include the chemicals in rubber gloves.
Topical medication sites
Allergic contact dermatitis is frequent in the perianal area as a result of the use of sensitizing medications and remedies (eg, topical benzocaine). Topical medications are also important causes of allergic contact dermatitis in cases of otitis externa. Allergy to chemicals in ophthalmologic preparations may provoke dermatitis around the eyes.
Airborne allergic contact dermatitis
Chemicals in the air may produce airborne allergic contact dermatitis. This dermatitis usually occurs maximally on the eyelids, but it may affect other areas exposed to chemicals in the air, particularly the head and the neck.
Hair dyes
Hair dye—in particular, the component p-phenylenediamine (PPD)—may trigger allergic contact dermatitis. Individuals allergic to hair dyes typically develop the most severe dermatitis on the ears and adjoining face rather than on the scalp.
Stasis dermatitis and stasis ulcers
Individuals with stasis dermatitis and stasis ulcers are at high risk for developing allergic contact dermatitis to topical medications applied to inflamed or ulcerated skin (see the image below). The chronicity of this condition and the frequent occlusion of applied medications contribute to the high risk of allergic contact dermatitis to medicament (eg, neomycin) in these patients.
Individuals may develop widespread dermatitis from topical medications applied to leg ulcers or from cross-reacting systemic medications administered intravenously. For example, a patient allergic to neomycin may develop systemic contact dermatitis if treated with intravenous gentamicin.
Chronic stasis dermatitis with allergic contact dermatitis to quaternium-15, a preservative in moisturizer. Allergic contact dermatitis produces areas of erythema in areas of atrophie blanche and varicose veins.
Erythema multiforme
Erythema multiforme (EM) is a severe cutaneous reaction with targetoid lesions that occurs primarily after exposure to certain medications or is triggered by infection, most commonly by herpes simplex virus. Rare cases of EM have been reported after allergic contact dermatitis resulting from exposure to poison ivy, [20] tropical woods, nickel, and hair dye (see the image below).
Intraoral metal contact allergy may result in mucositis that mimics lichen planus, which has an association with intraoral squamous cell carcinoma. Intraoral squamous cell carcinoma adjacent to a dental restoration containing a metal to which the patient was allergic has been reported. [21]
Allergic contact dermatitis may be a direct trigger for skin ulceration in patients with venous insufficiency. Early diagnosis and treatment of allergic contact dermatitis may prevent the development of venous ulcers.
Complications
Darkly pigmented individuals may develop areas of hyperpigmentation or hypopigmentation from allergic contact dermatitis. Occasionally, they may develop depigmentation at sites of allergic contact dermatitis to certain chemicals.
Occasionally, allergic contact dermatitis is complicated by secondary bacterial infection, which may be treated by the appropriate systemic antibiotic.
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Chronic stasis dermatitis with allergic contact dermatitis to quaternium-15, a preservative in moisturizer. Allergic contact dermatitis produces areas of erythema in areas of atrophie blanche and varicose veins.
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Erythema multiformelike reaction that developed acutely following hair dying.
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Allergic contact dermatitis to nickel in a necklace.
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Severe allergic contact dermatitis resulting from preservatives in sunscreen. Patch testing was negative to the active ingredients in the sunscreen.
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Onycholysis developing from allergic contact dermatitis to formaldehyde used to harden nails.
