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Contact dermatitis
is acute inflammation of the skin caused by irritants or allergens.
The primary symptom is pruritus; skin changes range from erythema
to blistering and ulceration, often on or near the hands but occurring
on any exposed skin surface. Diagnosis is by exposure history, examination,
and sometimes skin patch testing. Treatment entails antipruritics, topical
corticosteroids, and avoidance of causes.
Etiology
and Pathophysiology
Irritant contact
dermatitis (ICD):
ICD accounts for 80% of all cases of contact dermatitis (CD). It is a nonspecific inflammatory reaction to substances contacting the skin; the immune system is not activated. Numerous substances are involved, including chemicals (eg, acids, alkalis, solvents, metal salts), soaps (eg, abrasives, detergents), plants (eg, poinsettias, peppers), and body fluids (eg, urine, saliva). Properties of the irritant (extreme pH, solubility in the lipid film on skin), environment (low humidity, high temperature, high friction), and patient (very young or old) influence the likelihood of developing ICD. ICD is more common in atopic patients, in whom ICD also may initiate immunologic sensitization and hence allergic CD.
Phototoxic dermatitis (see Reactions to Sunlight: Chemical photosensitivity) is a variant in which topical (eg, perfumes, coal tar ) or ingested (eg, psoralens) agents generate damaging free radicals and inflammatory mediators only after absorption of ultraviolet light.
Allergic contact
dermatitis (ACD):
ACD is a type IV cell-mediated hypersensitivity reaction that has 2 phases: sensitization to an antigen and response on reexposure. In the sensitization phase, allergens are captured by Langerhans' cells (dendritic epidermal cells), which migrate to regional lymph nodes where they process and present the antigen to T cells. The process may be brief (6 to 10 days for strong sensitizers such as poison ivy) or prolonged (years for weak sensitizers such as sunscreens, fragrances, and glucocorticoids). Sensitized T cells then migrate back to the epidermis and activate on re-exposure to the allergen, releasing cytokines, recruiting inflammatory cells, and leading to the characteristic symptoms and signs of ACD.
In autoeczematization, epidermal T cells activated by allergen migrate locally or through the circulation to cause dermatitis at sites remote from the initial trigger. However, contact with fluid from vesicles or blisters cannot trigger a reaction elsewhere on the patient or on another person.
Multiple allergens cause ACD (see Table 2: Dermatitis: Causes of Allergic Contact Dermatitis ), and cross-sensitization among agents is common (eg, between benzocaine and paraphenylene diamine).
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Table 2
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Causes of Allergic Contact
Dermatitis
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Cause
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Examples
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Airborne substances
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Ragweed pollen, insecticide spray
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Chemicals used in shoe or clothing manufacturing
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Particularly agents used in leather and rubber processing; tanning agents in shoes; rubber accelerators and antioxidants in gloves, shoes, underpants, and other apparel; formaldehyde in durable-press finishes
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Cosmetics
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Depilatories, nail polish, deodorant
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Dyes
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p-Phenylenediamine (hair and textile dyes) and others
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Fragrances
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Various compounds; ubiquitous in toiletries, soaps, scented household products
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Industrial agents
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Many compounds, including acrylic monomers, epoxy compounds, vat dyes, rubber accelerators, formaldehyde (in plastics and adhesives)
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Ingredients in topical drugs:
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Bacitracin , neomycin , penicillin, sulfonamides,
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Diphenhydramine , promethazine
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Benzocaine
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Thimerosal, hexachlorophene
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Ethylenediamine and derivatives
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Latex
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Latex gloves, condoms, catheters, balloons
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Metal compounds
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Numerous occupational exposures. Also personal items, such as belt buckle, watch buckle, and jewelry
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Plants
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Poison ivy, oak, and sumac; ragweed; primrose; cashew shells; mango peel
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ACD variants include photoallergic CD and systemically induced ACD. In photoallergic CD (see Reactions to Sunlight: Chemical photosensitivity), a substance becomes sensitizing only after it undergoes structural change triggered by ultraviolet light. Typical causes include aftershave lotions, sunscreens, and topical sulfonamides. Reactions may extend to non–sun-exposed skin. In systemically induced ACD, ingestion of an allergen after topical sensitization causes diffuse dermatitis (eg, oral diphenhydramine after sensitization with topical diphenhydramine ).
Symptoms and Signs
ICD is more painful than pruritic. Signs range from mild erythema to hemorrhage, crusting, erosion, pustules, bullae, and edema.
In ACD, the primary symptom is intense pruritus; pain is usually the result of excoriation or infection. Skin changes range from transient erythema through vesiculation to severe swelling with bullae and/or ulceration. Changes often occur in a pattern and/or distribution that suggest a specific exposure, such as linear streaking on an arm or leg (eg, from brushing against poison ivy) or circumferential erythema (under a wristwatch or waistband). Any surface may be involved, but hands are most common due to handling and touching potential allergens. With airborne exposure (eg, perfume aerosols), areas not covered by clothing are predominantly involved. The dermatitis is typically limited to the site of contact but may later spread due to scratching and autoeczematization. In systemically induced ACD, skin changes may be distributed over the entire body.
Diagnosis
CD can often be diagnosed by skin changes and exposure history. The patient's occupation, hobbies, household duties, vacations, clothing, topical drug use, cosmetics, and spouse's activities must be considered. The “use test,” in which a suspected agent is applied far from the original area of dermatitis usually on the flexor forearm, is useful when perfumes, shampoos, or other home agents are suspected.
Patch testing is indicated when ACD is suspected and does not respond to treatment. In patch testing, standard contact allergens are applied to the upper back using adhesive-mounted patches containing minute amounts of allergen or plastic (Finn) chambers containing allergen held in place with porous tape. Thin-layer rapid use epicutaneous (T.R.U.E.) patch testing involves 2 adhesive strips that can be applied and interpreted by any provider. Skin under the patches is evaluated 48 and 96 h after application. False-positives are seen when concentrations provoke an irritant rather than allergic reaction, when reaction to one antigen triggers a nonspecific reaction to others, or with cross-reacting antigens. False-negatives are seen when patch allergens do not include the offending antigen. Definitive diagnosis requires a history of exposure to the test agent in the original area of dermatitis.
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| Common Allergens Used in Patch Testing |
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Agent
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Sources
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Balsam of Peru
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A flavoring agent for drinks and tobacco, as well as a fixative and fragrance in perfumes; also found in many topical drugs, dental agents, etc.; chief allergens are esters of cinnamic and benzoic acid, vanillin; cross-reactions with colophony (rosin) and balsam of Tolu, the cinnamates, benzoates, styrax, and tincture of benzoin; probably also some phototoxicity
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Black rubber mix
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In rubber; may cross-react with hair dyes
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Caine mix
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Contains 3 topical anesthetics: benzocaine, dibucaine hydrochloride, and tetracaine hydrochloride; often used in dentistry but also widely found and used in topical preparations to reduce itching, pain, and stinging; widely used in hemorrhoidal preparations and cough syrups
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Carba mix
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Used as an accelerator in rubber, rubber glues, vinyl, and some pesticides
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Cl+ Me- Isothiazolinone
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Found in cosmetics and skin care products, some drugs, household cleaning products, and certain industrial fluids and greases
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Cobalt dichloride
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Found in some paints, cement, metal, metal-plated objects; coactivity with nickel is not cross sensitivity
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Colophony (rosin)
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Used by string players (violinists are especially prone to allergy), baseball players, and bowlers; derived from several conifer species; found in cosmetics, adhesives, lacquers, varnishes, soldering fluxes, paper, and many other industrial products
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Epoxy resin
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A low molecular weight (340) epoxy based on bisphenol A and epichlorohydrin; the resin is a sensitizer only when uncured or incompletely cured
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Ethylenediamine
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Used as an emulsifier and stabilizer in certain topical drugs, eye drops, some industrial solvents, curing agents for certain plastics, and anti-corrosion agents
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Formaldehyde
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Released by quaternium-15, a germicidal agent, and occasionally by imidazolidinyl urea; used widely in formulation of plastics, resins for clothing, glues, adhesives
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Fragrance mix
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Contains alpha amyl cinnamic alcohol, cinnamic aldehyde, cinnamic alcohol, oak moss absolute, hydroxycitronellal, eugenol, isoeugenol, and geraniol; found in many toiletries, soaps, after-shave lotions, shampoos, and scented household products, and in many industrial products (eg, cutting fluids)
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Mercaptobenzothiazole
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Found in rubber, adhesives, and coolants
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Mercapto mix
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Found in rubber, glues, coolants, and other industrial products
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Neomycin sulfate
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Found in topical antibiotics, first-aid creams, ear drops, and nose drops; patch test reaction may be somewhat delayed (about 4-5 days) so reading should be done at 7 days when possible
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Nickel sulfate
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Found in jewelry, dentures, scissors, razors, eyeglass frames, silverware, foods (eg, canned foods, foods cooked in nickel utensils, herring, oyster, asparagus, beans, mushrooms, onions, others)
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Paraben mix
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Five parabens: methyl, ethyl, propyl, butyl, and benzyl parahydroxybenzoates; they are the most common preservatives used worldwide and are found in numerous creams and cosmetics and in some industrial oils, fats, and glues
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Potassium dichromate
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Found in cement in minute amounts, in tanning solutions for leather, and in safety matches; used in photography, electroplating solutions, many anti-corrosives, paints, glues, pigments, and some detergents
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p-Phenylenediamine (PPD)
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Found in hair dyes, some inks, photo developers, and textile dyes
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p-Tert butylphenol formaldehyde resin
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A resin formed by condensation between p-tert-butylphenol and formaldehyde; found in leather finishes, especially shoes, paper, fabrics, rockwood, furniture, as well as certain glues
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Quaternium
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Common preservative found in cosmetics and in some household cleaners and polishes
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Quinolone mix
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Contains clioquinol and chlorquinaldol, antimicrobials found in certain medicated creams and ointments, medicated bandages, and veterinary products
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Thimerosal
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Preservative in contact lens solutions, certain cosmetics, nose and ear drops, and injectables; source often not found
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Thiuram mix
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Common rubber allergen; also found in adhesives, certain pesticides, and drugs (eg, disulfiram)
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Prognosis
and Treatment
Resolution may take up to 3 wk. Reactivity is usually lifelong. Patients with photoallergic CD can have flares for years when exposed to sun (persistent light reaction).
CD is treated by avoiding the trigger; patients with photosensitive CD should avoid exposure to sun. Topical treatment includes cool compresses (saline or Burow's) and corticosteroids; patients with mild to moderate ACD are given mid-potency topical corticosteroids (eg, triamcinolone 0.1% ointment or betamethasone valerate cream 0.1%). Oral corticosteroids (eg, prednisone 60 mg once/day for 7 to 14 days) can be used for severe blistering or extensive disease. Systemic antihistamines (eg, hydroxyzine , diphenhydramine ) help pruritus; antihistamines with low anticholinergic potency are not as effective. Wet-to-dry dressings can soothe oozing blisters, dry the skin, and promote healing.
Last full review/revision November 2005
Content last modified November 2005
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