United States statistics
The National Health and Nutrition Examination Survey (NHANES) estimated the prevalence of contact dermatitis to be 13.6 cases per 1000 population, using physical examinations by dermatologists of a selected sample of patients. NHANES underreported the prevalence compared with the physical examination findings.
The National Ambulatory Medical Care Survey conducted in 1995 estimated 8.4 million outpatient visits to American physicians for contact dermatitis. This was the second most frequent dermatologic diagnosis. Of office visits to dermatologists, 9% are for dermatitis. At a student health center dermatology clinic, 3.1% of patients presented for allergic contact dermatitis, and 2.3% presented for irritant contact dermatitis.
The TRUE test Web site can provide accurate basic information on common allergens. The Contact Allergen Management Program is provided as a service to the American Contact Dermatitis Society (ACDS) members and is particularly valuable for allergens found in topical skin care products. The Contact Allergen Management Program (CAMP) database contains more than 8100 known ingredients cataloged in more than 5500 commercial skincare products and is available as a Smartphone application.
A Swedish study found that prevalence of allergic contact dermatitis of the hands was 2.7 cases per 1000 population. A Dutch study found that prevalence of allergic contact dermatitis of the hands was 12 cases per 1000 population.
Race, sex, and age-related demographics
No racial predilection exists for allergic contact dermatitis. Allergic contact dermatitis is more common in women than in men. This predominantly is a result of allergy to nickel, which is much more common in women than in men in most countries.
Allergic contact dermatitis may occur in neonates. In elderly individuals, the development of allergic contact dermatitis may be delayed somewhat, but the dermatitis may be more persistent once developed. Contact allergy to topical medicaments is more common in persons older than 70 years. 
The prognosis depends on how well the affected individual can avoid the offending allergen. 
Individuals with allergic contact dermatitis may have persistent or relapsing dermatitis, particularly if the material(s) to which they are allergic is not identified or if they continue to practice skin care that is no longer appropriate (ie, they continue to use harsh chemicals to wash their skin, they do not apply creams with ceramides or bland emollients to protect their skin).
The longer an individual has severe dermatitis, the longer it is believed it will take the dermatitis to resolve once the cause is identified.
Some individuals have persistent dermatitis following allergic contact dermatitis, which appears to be true especially in individuals allergic to chromates.
A particular problem is neurodermatitis (lichen simplex chronicus), in which individuals repeatedly rub or scratch an area initially affected by allergic contact dermatitis.
Death from allergic contact dermatitis is rare in the United States. Allergic contact dermatitis to the weed wild feverfew caused deaths in India when the seeds contaminated wheat shipments to India. This plant then became widespread and a primary cause of severe airborne allergic contact dermatitis.
Patients have the best prognosis when they are able to remember the materials to which they are allergic and how to avoid further exposures. Provide patients with as much information as possible concerning the chemical to which they are allergic, including all known names of the chemical. Web sites, Smartphone applications, standard textbooks, and the TRUE test kit contain basic information about the chemicals.
Susceptible individuals need to read the list of ingredients before applying cosmetic products to their skin, since preservative chemicals are used widely in consumer, medical, and workplace products. The same chemical may have different names when used for consumer or industrial purposes.
Provide pamphlets with color pictures of poison ivy to individuals allergic to the plant. The American Academy of Dermatology also has pamphlets on allergic contact dermatitis and hand eczema.
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. 
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.
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.
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.
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.
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).
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 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 (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.
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 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 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.
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,  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. 
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.
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.
Contact dermatitis from allergy must be differentiated from contact dermatitis due to irritation, as well as other forms of dermatitis. In addition, the specific substance to which the patient is sensitive needs to be identified.
Contact Urticaria Syndrome
Drug-Induced Bullous Disorders
Irritant Contact Dermatitis
Nummular Dermatitis (Nummular Eczema)
Transient Acantholytic Dermatosis
A guideline summary on allergy testing is available from the American Academy of Allergy, Asthma and Immunology, American College of Allergy, Asthma and Immunology (Allergy Diagnostic Testing: An Updated Practice Parameter). 
Potassium hydroxide preparation and/or fungal culture to exclude tinea are often indicated for dermatitis of the hands and feet. This will identify disorders such as tinea pedis.
Patch testing [23, 24, 25] is required to identify the external chemicals to which the person is allergic. The greatest quality-of-life benefits from patch testing occur in patients with recurrent or chronic allergic contact dermatitis (ACD). Patch testing is most cost-effective and reduces the cost of therapy in patients with severe allergic contact dermatitis.
Patch testing should be performed by healthcare providers trained in the proper technique. Most dermatologists can perform patch testing using the TRUE test, which can identify relevant allergies in as many as one half of affected patients. More extensive patch testing is indicated to identify allergies to chemicals not found in the TRUE test. Such testing typically is available only in a limited number of dermatology offices and clinics.
The patch testing procedure is as follows:
Small amounts of appropriate labeled dilutions of chemicals are applied to the skin and occluded for 2 days
Patch tests may be left on for 3 days before removal
For reasons of scheduling, a chemical must remain under a skin patch for a minimum of 1 day to produce a positive patch test reaction 2-7 days following initial application
The patch test must be read not only at 48 hours, when the patch tests customarily are removed, but again between 72 hours and 1 week following initial application
Individuals with suspected allergic contact dermatitis without positive reactions on the TRUE test or with chronic dermatitis or relapsing dermatitis, despite avoiding chemicals to which they are allergic (identified on TRUE test), need additional patch testing. Many individuals have more than 1 contact allergy and may be allergic to 1 or more chemicals found on the TRUE test and on special allergen trays or series.
Testing reactions to more allergens increases accuracy of the diagnosis of allergic contact dermatitis. Selection of allergens for testing requires consideration of the patient’s history and access to appropriate environmental contactants.
Certain chemicals (eg, neomycin) typically produce delayed positive patch test reactions at 4 days or later following initial application. A tendency exists for elderly patients to manifest positive patch test reactions later than younger patients. Do not perform patch testing on patients taking more than 15 mg/d of prednisone. Oral antihistamines may be used during the patch test period if required.
Angry back syndrome or excited skin syndrome may occur. If a patient has a large number of positive patch test reactions, retesting the patient sequentially to a small series of these allergens may be necessary to exclude nonspecific false-positive reactions. The syndrome most likely occurs in individuals who have active dermatitis at the time of patch testing or who have a strong positive patch test reaction, both of which may induce local skin hyperreactivity in the area where patches were applied.
Additional patch test series or sets include the following:
Corticosteroids, particularly tixocortol pivalate and budesonide
Ingredients in cosmetics not found in the TRUE test
Chemicals used in dentistry that may produce mucosal and lip dermatitis in dental clients or that may produce chronic dermatitis of the hands in dentists and dental team members
Chemicals used in hairdressing that may produce facial, ear, and neck dermatitis in clients or chronic hand dermatitis or eyelid dermatitis in hairdressers
Fragrances found in cosmetics and a wide range of consumer products
Important allergens not found in the TRUE test that are frequent causes of allergic contact dermatitis are as follows:
Acrylates used in dentistry, artificial nails, and printing
Chemicals used in baking
Pesticides (many cases of dermatitis attributed to pesticides result from other causes, particularly from plants such as poison ivy)
Chemicals used in machining, eg, cutting oils and fluids
Photographic chemicals used by photographers and photographic developers
Chemicals in plastics and glues
Chemicals found in rubber products not included in the TRUE test
Chemicals in shoes and clothing
Ultraviolet (UV) protective ingredients in sunscreens
Other chemicals producing photo allergic contact dermatitis
The chemicals listed above are tested under Finn chambers, allergEAZE chambers, or the IQ Chamber patch test. In photopatch testing, the chemicals are applied in duplicate sets. One set receives 10 J/cm2 of UV-A (or 1 J/cm2 less than the minimum erythema dose, whichever is lowest) 24 hours after application of the allergens. The other series is protected from UV exposure to differentiate allergic contact dermatitis and photo-accentuated allergic contact dermatitis from photo-allergic contact dermatitis. Both sets are read at 48 hours after application, as well as at an additional time point as in routine patch testing.
The safety of patch testing in pregnancy has not been studied; however, the minute amounts of allergens applied appear unlikely to be absorbed in sufficient amounts to harm the fetus. Nonetheless, as with all treatments in pregnant women, the benefits of testing should be weighed against any potential, albeit undocumented, risk.
Individuals with atopic dermatitis may have more positive patch-test reactions to ingredients in personal care products, to the topical steroids that they use, as well as to antibiotics.