Since contact dermatitis relies on an irritant or an allergen to initiate the reaction, it is important for the patient to identify the responsible agent and avoid it. This can be accomplished by having patch tests, one of various methods commonly known as allergy testing. The top three allergens found in patch tests from 2005–06 were: nickel sulfate (19.0%), Myroxylon pereirae (Balsam of Peru, 11.9%), and fragrance mix I (11.5%).

The patient must know where the irritant or allergen is found to be able to avoid it. It is important to also note that chemicals sometimes have several different names, and do not always appear on labels.

The distinction between the various types of contact dermatitis is based on a number of factors. The morphology of the tissues, the histology, and immunologic findings are all used in diagnosis of the form of the condition. However, as suggested previously, there is some confusion in the distinction of the different forms of contact dermatitis. Using histology on its own is insufficient, as these findings have been acknowledged not to distinguish, and even positive patch testing does not rule out the existence of an irritant form of dermatitis as well as an immunological one.

Diagnosing allergic contact dermatitis is primarily based on physical exam and medical history. In some cases doctors can establish an accurate diagnosis based on the symptoms that the patient experiences and on the rash's appearance. In the case of a single episode of allergic contact dermatitis, this is all that is necessary. Chronic and/or intermittent rashes which are not readily explained by history and physical exam often will benefit from further testing.

A patch test (contact delayed hypersensitivity allergy test) is a commonly used examination to determine the exact cause of an allergic contact dermatitis. According to the American Academy of Allergy, Asthma, and Immunology, "patch testing is the gold standard for contact allergen identification".

The patch test consists of applying small quantities of potential allergens to small patches and which are then placed on the skin. After two days, they are removed and if a skin reaction occurred to one of the substances applied, a raised bump will be noticeable underneath the patch. The tests are again read at 72 or 96 hours after application.

Patch testing is used for patients who have chronic, recurring contact dermatitis. Other tests that may be used to diagnose contact dermatitis and rule out other potential causes of the symptoms include a skin biopsy and culture of the skin lesion.

Diagnosis of eczema is based mostly on the history and physical examination. In uncertain cases, skin biopsy may be useful. Those with eczema may be especially prone to misdiagnosis of food allergies.

Patch tests are used in the diagnosis of allergic contact dermatitis.

There is no good evidence that a mother's diet during pregnancy, the formula used, or breastfeeding changes the risk. There is tentative evidence that probiotics in infancy may reduce rates but it is insufficient to recommend its use.

People with eczema should not get the smallpox vaccination due to risk of developing eczema vaccinatum, a potentially severe and sometimes fatal complication.

In an industrial setting the employer has a duty of care to its worker to provide the correct level of safety equipment to mitigate exposure to harmful irritants. This can take the form of protective clothing, gloves, or barrier cream, depending on the working environment.

Topical antibiotics should not be used to prevent infection in wounds after surgery. When they are used, it is inappropriate, and the person recovering from surgery is at significantly increased risk of developing contact dermatitis.

In adults, the prevalence of IgE sensitization to allergens from house dust mite and cat, but not grass, seem to decrease over time as people age. However, the biological reasons for these changes are not fully understood.

The clinical expression of the dermatitis can be mitigated by avoidance of the allergen. Through compliance with avoidance measures, the immune system can become less stimulated. The key to avoidance is proper evaluation and detection of the inciting allergen. However, once the immune system registers the allergen, the recognition is permanent.

The first step in treating the condition is appropriate recognition of the clinical problem, followed by identification of the culprit chemical and the source of that chemical. Corticosteroid creams should be used carefully and according to the prescribed directions because when overused over longer periods of time they can cause thinning of the skin. Also, in some instances such as poison ivy dermatitis calamine lotion and cool oatmeal baths may relieve itching.

Usually, severe cases are treated with systemic corticosteroids which may be tapered gradually, with various dosing schedules ranging from a total of 12 – 20 days to prevent the recurrence of the rash (while the chemical allergen is still in the skin, up to 3 weeks, as well as a topical corticosteroid. Tacrolimus ointment or pimecrolimus cream can also be used additionally to the corticosteroid creams or instead of these. Oral antihistamines such as diphenhydramine or hydroxyzine may also be used in more severe cases to relieve the intense itching. Topical antihistamines are not advised as there might be a second skin reaction (treatment associated contact dermatitis) from the lotion itself.

The other symptoms caused by allergic contact dermatitis may be eased with cool compresses to stop the itching. It is vital for treatment success that the trigger be identified and avoided. The discomfort caused by the symptoms may be relieved by wearing smooth-textured cotton clothing to avoid frictional skin irritation or by avoiding soaps with perfumes and dyes.

Commonly, the symptoms may resolve without treatment in 2 to 4 weeks but specific medication may hasten the healing as long as the trigger is avoided. Also, the condition might become chronic if the allergen is not detected and avoided.

A rarely cited double-blind study in 1982 reported that a course of oral urushiol usually hyposensitized subjects.

With no particular affinity to any particular ethnic group, seen in all age groups and equally amongst males and females, the precise prevalence is not known.

Corticosteroids: For years, there was no treatment for atopic eczema. Atopy was believed to be allergic in origin due to the patients’ extremely high serum IgE levels, but standard therapies at the time did not help. Oral prednisone was sometimes prescribed for severe cases. Wet wraps (covering the patients with gauze) were sometimes used in hospitals to control itching. However, the discovery of corticosteroids in the 1950s, and their subsequent incorporation in topical creams and ointments, provided a significant advancement in the treatment of atopic eczema and other conditions. Thus, the use of topical steroids avoided many of the undesirable side-effects of systemic administration of corticosteroids. Topical steroids control the itching and the rash that accompany atopic eczema. Side-effects of topical steroid use are plentiful, and the patient is advised to use topical steroids in moderation and only as needed.

Immune modulators: Pimecrolimus and tacrolimus creams and ointments became available in the 1980s and are sometimes prescribed for atopic eczema. They act by interfering with T cells but have been linked to the development of cancer.

Avoiding dry skin: Dry skin is a common feature of patients with atopic eczema (see also eczema for information) and can exacerbate atopic eczema.

Avoiding allergens and irritants: See eczema for information.

Effective management of allergic diseases relies on the ability to make an accurate diagnosis. Allergy testing can help confirm or rule out allergies. Correct diagnosis, counseling, and avoidance advice based on valid allergy test results reduces the incidence of symptoms and need for medications, and improves quality of life. To assess the presence of allergen-specific IgE antibodies, two different methods can be used: a skin prick test, or an allergy blood test. Both methods are recommended, and they have similar diagnostic value.

Skin prick tests and blood tests are equally cost-effective, and health economic evidence shows that both tests were cost-effective compared with no test. Also, early and more accurate diagnoses save cost due to reduced consultations, referrals to secondary care, misdiagnosis, and emergency admissions.

Allergy undergoes dynamic changes over time. Regular allergy testing of relevant allergens provides information on if and how patient management can be changed, in order to improve health and quality of life. Annual testing is often the practice for determining whether allergy to milk, egg, soy, and wheat have been outgrown, and the testing interval is extended to 2–3 years for allergy to peanut, tree nuts, fish, and crustacean shellfish. Results of follow-up testing can guide decision-making regarding whether and when it is safe to introduce or re-introduce allergenic food into the diet.

Treatment consists of two phases: stopping the urushiol contact that is causing the reaction (this must be done within minutes) and, later, reducing the pain and/or itching.

Primary treatment involves washing exposed skin thoroughly with soap, water, and friction as soon as possible after exposure is discovered. Soap or detergent is necessary because urushiol is an oil; friction, with a washcloth or something similar, is necessary because urushiol adheres strongly to the skin. Commercial removal preparations, which are available in areas where poison ivy grows, usually contain surfactants, such as the nonionic detergent Triton X-100, to solubilize urushiol; some products also contain abrasives.

The U.S. Food and Drug Administration recommends applying a wet compress or soaking the affected area in cool water; topical corticosteroids (available over-the-counter) or oral corticosteroids (available by prescription); and topical skin protectants, such as zinc acetate, zinc carbonate, zinc oxide, and calamine. Baking soda or colloidal oatmeal can relieve minor irritation and itching. Aluminium acetate, sometimes known as Burow's solution, can also ease the rash.

Showers or compresses using hot (but not scalding) water can relieve itching for up to several hours, though this "also taxes the skin's integrity, opening pores and generally making it more vulnerable", and is only useful for secondary treatment (not for cleaning urushiol from the skin, which should be done with cold water). People who have had a prior systemic reaction may be able to prevent subsequent exposure from turning systemic by avoiding heat and excitation of the circulatory system and applying moderate cold to any infected skin with biting pain.

Antihistamine and hydrocortisone creams, or oral antihistamines in severe cases, can alleviate the symptoms of a developed rash. Nonprescription oral diphenhydramine (U.S. trade name Benadryl) is the most commonly suggested antihistamine. Topical formulations containing diphenhydramine are also available but may further irritate the skin.

In cases of extreme symptoms, steroids such as prednisone or triamcinolone are sometimes administered to attenuate the immune response and prevent long-term skin damage, especially if the eyes are involved. Prednisone is the most commonly prescribed systemic treatment but can cause serious adrenal suppression, so it must be taken carefully and tapered off slowly. If bacterial secondary infection of affected areas occurs, antibiotics may also be necessary.

Scrubbing with plain soap and cold water will remove urushiol from skin if it is done within a few minutes of exposure. Many home remedies and commercial products (e.g., Tecnu, Zanfel) also claim to prevent urushiol rashes after exposure. A study that compared Tecnu ($1.25/oz.) with Goop Hand Cleaner or Dial Ultra Dishwashing Soap ($0.07/oz.) found that differences among the three—in the range of 56–70% improvement over no treatment—were nonsignificant ("P" > 0.05), but that improvement over no treatment was significant at the same level of confidence.

Further observations:

- Ordinary laundering with laundry detergent will remove urushiol from most clothing but not from leather or suede.

- The fluid from the resulting blisters does "not" spread urushiol to others.

- Blisters should be left unbroken during healing.

- Poison ivy and poison oak are still harmful when the leaves have fallen off, as the toxic residue is persistent, and exposure to any parts of plants containing urushiol can cause a rash at any time of the year.

- Ice, cold water, cooling lotions, and cold air do "not" help cure poison ivy rashes, but cooling can reduce inflammation and soothe the itch.

- Results for jewelweed as a natural agent for treatment are conflicting. Some studies indicate that it "failed to decrease symptoms of poison ivy dermatitis" [1980] and had "no prophylactic effect" [1997]. The juice of the leaves and stems of Impatiens capensis is a traditional Native American remedy for skin rashes, including poison ivy and such use has been supported by at least one peer-reviewed study, as recently as 2012.

An allergy blood test is quick and simple, and can be ordered by a licensed health care provider ("e.g.", an allergy specialist), GP, or PED. Unlike skin-prick testing, a blood test can be performed irrespective of age, skin condition, medication, symptom, disease activity, and pregnancy. Adults and children of any age can take an allergy blood test. For babies and very young children, a single needle stick for allergy blood testing is often more gentle than several skin tests.

An allergy blood test is available through most laboratories. A sample of the patient's blood is sent to a laboratory for analysis, and the results are sent back a few days later. Multiple allergens can be detected with a single blood sample. Allergy blood tests are very safe, since the person is not exposed to any allergens during the testing procedure.

The test measures the concentration of specific IgE antibodies in the blood. Quantitative IgE test results increase the possibility of ranking how different substances may affect symptoms. A rule of thumb is that the higher the IgE antibody value, the greater the likelihood of symptoms. Allergens found at low levels that today do not result in symptoms can nevertheless help predict future symptom development. The quantitative allergy blood result can help determine what a patient is allergic to, help predict and follow the disease development, estimate the risk of a severe reaction, and explain cross-reactivity.

A low total IgE level is not adequate to rule out sensitization to commonly inhaled allergens. Statistical methods, such as ROC curves, predictive value calculations, and likelihood ratios have been used to examine the relationship of various testing methods to each other. These methods have shown that patients with a high total IgE have a high probability of allergic sensitization, but further investigation with allergy tests for specific IgE antibodies for a carefully chosen of allergens is often warranted.

Laboratory methods to measure specific IgE antibodies for allergy testing include enzyme-linked immunosorbent assay (ELISA, or EIA), radioallergosorbent test (RAST) and fluorescent enzyme immunoassay (FEIA).

Other rashes that occur in a widespread distribution can look like an id reaction. These include atopic dermatitis, contact dermatitis, dyshidrosis, photodermatitis, scabies and drug eruptions.

Dermographism can be treated by substances (i.e. an antihistamine) which prevent histamine from causing the reaction. These may need to be given as a combination of H antagonists, or possibly with an H-receptor antagonist such as cimetidine.

OTC Vitamin C, 1000 mg daily, increases histamine degradation and removal.

Not taking hot baths or showers may help if it is generalized (all over) and possibly for localized cases (in a specific area). If taking hot showers helps, it may be a condition called shower eczema. If it affects mainly the head, it may be psoriasis. In rare cases, allergy tests may uncover substances the patient is allergic to.

While cromoglycate, which prevents histamine from being released from mast cells, is used topically in rhinitis and asthma, it is not effective orally for treating chronic urticaria.

Prevention includes avoiding exposure to the sun and wearing sun block on the affected area.

- Cover up: wear long sleeves, slacks, and a wide-brimmed hat whenever harsh exposure is probable

- Avoid chemicals that may trigger a reaction

- Wear sunscreen at least factor 30 with a high UVA protection level

- Wear gloves and/or remain indoors after handling fruits or plants which increase sensitivity to light

A detailed history allows physicians to determine whether the presenting symptoms are due to an allergen or another source. Diagnostic tests such as conjunctival scrapings to look for eosinophils are helpful in determining the cause of the allergic response. Antihistamines, medication that stabilizes mast cells, and NSAIDs are safe and usually effective. Corticosteroids are reserved for more severe cases of ocular allergy disease, and their use should be monitored by an eye care physician due to possible side-effects. When an allergen is identified, the person should avoid the allergen as much as possible.

Skin prick testing is a common way of testing for an allergy. Other ways to test for allergies can be challenge testing, which consists in feeding a very small and measured amount of the allergen to the patient and monitor the reaction (O'Neil, Zanovec and Nickla). This should only be done by a doctor under surveillance.

If the allergen is encountered and the symptoms are mild, a cold compress can be used to provide relief.

Eyelid dermatitis is commonly related to atopic dermatitis or allergic contact dermatitis. Volatile substances, tosylamide, epoxy hardeners, insect sprays, and lemon peel oil may be implicated, with many cases of eyelid contact dermatitis being caused by substances transferred by the hands to the eyelids.

For some people, the sensitivity is so extreme that replacement of latex products with products made from alternative materials may still result in a reaction if the products are manufactured in the same facility as the latex-containing products, due to trace quantities of natural rubber latex on the non-latex products.

Estimates of latex sensitivity in the general population range from 0.8% to 8.2%.

To confirm OAS, the suspected food is consumed in a normal way. The period of observation after ingestion and symptoms are recorded. If other co factors like combined foods are required, this is also replicated in the test. For example, if the individual always develops symptoms after eating followed by exercise, then this is replicated in the laboratory.

Many people have no idea that they have OAS. However, if swelling, tingling or pain develops while eating certain foods, then it is wise to see an allergy specialist. Before a diagnosis can be made, keep a food diary. This is important as the physician can then perform an allergy test. Before testing is started, a comprehensive history is obtained so that random testing is avoided. The diagnosis of OAS may involve skin prick tests, blood tests, patch tests or oral challenges. When OAS is suspected, the oral challenge test is ideal.

The aim of treatment is to relieve the allergy-induced itch and to remove the fleas from the pet and its home environment. In some cases, secondary bacterial or yeast infections will also need treatment before the itching subsides. Environmental flea control includes using flea foggers or bombs, vacuuming, and treating pet bedding by washing on a hot cycle (over 60 degrees Celsius) in the washing machine. The current on-pet treatment recommended by veterinary dermatologists is spinosad (Comfortis) monthly and nitenpyram (Capstar or generics) every 48 hours until improvement.

Many pets with FAD may also have other allergies, such as allergies to food, contact allergies, and atopic dermatitis.