Allergic Contact Dermatitis (Skin Allergies)
Physical: Acute ACD is characterized by pruritic papules and vesicles on an erythematous base. Lichenified pruritic plaques may manifest chronic ACD. Occasionally, ACD may affect the entire integument (ie, erythroderma, exfoliative dermatitis). The initial site of dermatitis often provides the best clue regarding the potential cause of ACD.
- Hands: Hands are an important site of ACD, particularly in the workplace. Common causes of allergic dermatitis on the hands include the chemicals in rubber gloves.
- Perianal: ACD is frequent in the perianal area as a result of the use of sensitizing medications and remedies (eg, topical benzocaine).
- Otitis externa: Topical medications are important causes of ACD in cases of otitis externa.
- Airborne ACD: Chemicals in the air may produce airborne ACD. 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.
- Ophthalmologic: Allergy to chemicals in ophthalmologic preparations may provoke dermatitis around the eyes.
- Hair dyes: 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 ACD to topical medications applied to inflamed or ulcerated skin (see Image 1). The chronicity of this condition and the frequent occlusion of applied medications contribute to the high risk of ACD 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.
- 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 ACD resulting from exposure to poison ivy, tropical woods, nickel, and hair dye (see Image 2).
Causes: Approximately 25 chemicals appear to be responsible for as many as one half of all cases of ACD.
- Poison ivy is the classic example of acute ACD in North America. ACD from poison ivy is characterized by linear streaks of acute dermatitis that develop where plant parts have been in direct contact with the skin.
- Nickel is the leading cause of ACD in the world. ACD to nickel typically is manifested by dermatitis at the sites where earrings or necklaces (see Image 3) containing nickel are worn or where metal objects containing nickel are in contact with the skin. Nickel may be considered a possible occupational allergen. Workers in whom nickel may be an occupational allergen primarily include hairdressers, retail clerks, caterers, domestic cleaners, and metalworkers. Individuals allergic to nickel occasionally may develop vesicles on the sides of the fingers (dyshidrotic hand eczema or pompholyx) from nickel in the diet.
- Allergy to 1 or more chemicals in rubber gloves is suggested in any individual with chronic hand dermatitis who is wearing them, unless patch testing demonstrates otherwise. ACD to chemicals in rubber gloves typically occurs maximally on the dorsal aspects of the hand. Usually, a cutoff of dermatitis occurs on the forearms where skin is no longer in contact with the gloves. Individuals allergic to chemicals in rubber gloves may develop dermatitis from other exposures to the chemicals (eg, under elastic waistbands).
- Individuals allergic to dyes and permanent press and wash-and-wear chemicals added to textiles typically develop dermatitis on the trunk, which occurs maximally on the lateral sides of the trunk but spares the vault of the axillae. Primary lesions may be small follicular papules or may be extensive plaques. Individuals in whom this ACD is suggested should be tested with a series of textile chemicals, particularly if routine patch testing reveals no allergy to formaldehyde. New clothing is most likely to provoke ACD, since most allergens decrease in concentration in clothing following repeated washings.
- Preservative chemicals added to cosmetics, moisturizers, and topical medications are major causes of ACD (see Image 4). The most widely used preservatives include parabens, which are not a frequent cause of ACD despite their wide use. The risk of ACD appears to be highest to quaternium-15, followed by ACD to isothiazolinones (Kathon CG).
- Formaldehyde is a major cause of ACD (see Image 5). Certain preservative chemicals widely used in shampoos, lotions, other moisturizers, and cosmetics are termed formaldehyde releasers (ie, quaternium-15 [Dowicil 200], imidazolidinyl urea [Germall 115]).
- Individuals may develop allergy to fragrances. Fragrances are found not only in perfumes, colognes, aftershaves, deodorants, and soaps, but also in numerous other products, often as a mask to camouflage an unpleasant odor. Unscented products may contain fragrance chemicals used as a component of the product and not labeled as fragrance. Individuals allergic to fragrances should use fragrance-free products. Unfortunately, the exact chemicals responsible for a fragrance in a product are not labeled. Four thousand different fragrance molecules are available to formulate perfumes. The fragrance industry is not required to release the names of ingredients used to compose a fragrance, even when individuals develop ACD to fragrances found in topical medications. Deodorants may be the most common cause of ACD to fragrances because they are applied to occlude skin. They often abrade in American women.
- Massage and physical therapists and geriatric nurses are at higher risk of occupational ACD to fragrances.
- In the last decade, it has become clear that many individuals with chronic dermatitis develop allergy to topical corticosteroids. Most affected individuals can be treated with some topical corticosteroids, but an individual can be allergic to all topical and systemic corticosteroids. Budesonide and tixocortol pivalate are useful patch test corticosteroids for identifying individuals allergic to topical corticosteroids.
- The risk of allergy to neomycin is related directly to the extent of its use in a population. The risk of allergy to neomycin is much higher when it is used to treat chronic stasis dermatitis than when it is used as a topical antibiotic on cuts and abrasions in children. Assume that individuals allergic to neomycin are allergic to chemically related aminoglycoside antibiotics (eg, gentamicin, tobramycin). Avoid these drugs both topically and systemically in individuals allergic to neomycin.
- Avoid topical use of benzocaine. Benzocaine is included in most standard patch test trays. Individuals allergic to benzocaine may safely use or be injected with Xylocaine, which does not cross-react with benzocaine.
- Many individuals complain of adverse reactions to sunscreens, but many of these individuals are not allergic to the sunscreen materials. They may be allergic to preservatives in these products (see Image 4) or may have nonspecific cutaneous irritation from these products.
- Occasionally, individuals develop photo ACD. ACD may be accentuated by ultraviolet (UV) light, or patients may develop an allergic reaction only when a chemical is present on the skin and when the skin is exposed sufficiently to ultraviolet light A (UV-A; 320-400 nm).