Merck Manual

Please confirm that you are not located inside the Russian Federation

honeypot link

Contact Dermatitis


Mercedes E. Gonzalez

, MD, University of Miami Miller School of Medicine

Last full review/revision Mar 2018| Content last modified Mar 2018
Click here for the Professional Version
Topic Resources

Contact dermatitis is skin inflammation caused by direct contact with a particular substance. The rash is very itchy, is confined to a specific area, and often has clearly defined boundaries.

Substances can cause skin inflammation by one of two mechanisms:

  • Irritation (irritant contact dermatitis)

  • Allergic reaction (allergic contact dermatitis)

Irritant contact dermatitis

This type of dermatitis, which accounts for 80% of all cases of contact dermatitis, occurs when a chemical substance causes direct damage to the skin. Irritant contact dermatitis is more painful than itchy. Typical irritating substances are.

  • Acids

  • Alkalis (such as drain cleaners)

  • Solvents (such as acetone in nail polish remover)

  • Strong soaps

  • Plants (such as poinsettias and peppers)

  • Body fluids (such as urine and saliva)

Some of these substances cause skin changes within a few minutes, whereas others require longer exposure. Even very mild soaps and detergents may irritate the skin of some people after frequent or prolonged contact. People vary in the sensitivity of their skin to irritants. The person's age (very young or very old) and environment (low humidity or high temperature) are other factors that influence whether irritant contact dermatitis develops.

Allergic contact dermatitis

This type of dermatitis is a reaction by the body's immune system to a substance contacting the skin. When the skin first comes into contact with the substance, the skin becomes sensitized to that substance. Sometimes a person can be sensitized by only one exposure, and other times sensitization occurs only after many exposures to a substance. After a person is sensitized, the next exposure causes intense itching and dermatitis within 4 to 24 hours, although some people, particularly older people, do not develop a reaction for 3 to 4 days.

Thousands of substances can result in allergic contact dermatitis. The most common include substances found in

  • Plants (such as poison ivy)

  • Rubber (including latex)

  • Antibiotics

  • Fragrances

  • Preservatives

  • Some metals (such as nickel and cobalt)

About 10% of women are allergic to nickel, a common component of jewelry. People may use (or be exposed to) substances for years without a problem, then suddenly develop an allergic reaction. Even ointments, creams, and lotions used to treat dermatitis can cause such a reaction. People may also develop dermatitis from many of the materials they touch while at work (occupational dermatitis).

Sometimes contact dermatitis results only after a person touches certain substances and then exposes the skin to sunlight (photoallergic or phototoxic contact dermatitis—see Chemical photosensitivity). Such substances include

  • Sunscreens

  • Aftershave lotions

  • Certain perfumes

  • Certain antibiotics applied to the skin

  • Coal tar

  • Oils

  • Plants

With photoallergic dermatitis, the reaction may spread to areas of skin that were not exposed to the sun.


Common Causes of Allergic Contact Dermatitis

  • Chemicals used in shoe or clothing manufacturing: Tanning agents in leather; rubber accelerators and antioxidants in gloves, shoes, undergarments, other apparel; dyes

    Cosmetics: Hair-removing chemicals (depilatories), hair dyes, nail polish, nail polish remover, deodorants, moisturizers, aftershave lotions, perfumes, sunscreens

    Drugs in skin creams: Antibiotics (bacitracin, sulfonamides, neomycin), antihistamines (diphenhydramine, promethazine), anesthetics (benzocaine), antiseptics (thimerosal), stabilizers

    Fragrances: Found in toiletries, soaps, and scented household products (such as detergent)

  • Metals: Nickel, cobalt, chromates, mercury, gold

  • Plants: Poison ivy, poison oak, poison sumac, ragweed, primrose, thistle, mango peels, cashew shells

  • Rubber (including latex): Gloves, condoms, catheters, balloons

  • Substances in the air: Ragweed pollen, insect sprays


Regardless of cause or type, contact dermatitis results in itching and a rash.

Allergic contact dermatitis usually causes severe itching.

Irritant contact dermatitis causes more pain than itching.

For both, the rash varies from a mild, short-lived redness to severe swelling and large blisters. Most commonly, the rash contains tiny blisters. The rash develops only in areas contacted by the substance. However, the rash appears earlier in thin, sensitive areas of skin, and later in areas of thicker skin or on skin that had less contact with the substance, giving the impression that the rash has spread.

The rash often occurs in a pattern that suggests exposure to a specific substance. For instance, poison ivy causes line-like streaks to form on the skin. Touching the rash or blister fluid cannot spread contact dermatitis to other people or to other parts of the body that did not make contact with the substance.


  • A doctor's evaluation and the person's history

  • Use test

  • Patch test

Determining the cause of contact dermatitis is not always easy. The person's occupation, hobbies, household duties, travel, clothing, use of topical drugs (drugs applied to the skin), cosmetics, and household members' activities must be considered. Most people are unaware of all the substances that touch their skin. Often, the location and pattern of the initial rash provide an important clue, particularly if the rash occurs under an item of clothing or jewelry or only in areas exposed to sunlight. However, many substances that people touch with their hands are unknowingly transferred to the face, where the more sensitive facial skin may react even if the hands do not.

The use test, in which a suspected substance is applied far from the original area of contact dermatitis (usually on the forearm), is useful when perfumes, shampoos, or other substances used in the home are suspected.

If a doctor suspects contact dermatitis and a process of elimination does not pinpoint the cause, patch testing can be done. For this test, small patches containing substances that commonly cause dermatitis are placed on the skin for 1 to 2 days to see whether a rash develops beneath one of them. Although useful, patch testing is complicated. People may be sensitive to many substances, and the substance they react to on a patch may not be the cause of their dermatitis. A doctor must decide which substances to test based on what a person might have been exposed to.


Contact dermatitis may take up to 3 weeks to resolve. Once people react to a substance, they usually react for the rest of their life. People who have photoallergic contact dermatitis may continue for years to have sun-induced flare-ups (called a persistent light reaction).


Contact dermatitis can be prevented by avoiding contact with the substances that cause dermatitis (causative substance). If contact does occur, the substance should be washed off immediately with soap and water. If people are at risk of ongoing exposure, gloves and protective clothing may be helpful. Barrier creams are also available that can block certain substances, such as poison ivy and epoxy resins, from contacting the skin. Desensitization with injections or tablets that contain the causative substance is not effective in preventing contact dermatitis.


  • Removal of substance causing the problem

  • Measures to relieve itching

  • Corticosteroids and sometimes antihistamines

Treatment of contact dermatitis is not effective until there is no further contact with the substance causing the problem. Once the substance is removed, the redness usually disappears after a week. Blisters may continue to ooze and form crusts, but they soon dry. Scaling, itching, and temporary thickening of the skin may last for days or weeks.

Itching and blisters can be relieved with a number of drugs applied to the skin or taken by mouth. In addition, small areas of dermatitis can be soothed by applying pieces of gauze or thin cloth dipped in cool water or aluminum acetate (Burow solution) several times a day for an hour. Larger areas may be treated with short, cool tub baths with or without colloidal oatmeal.

Often a corticosteroid is applied to the affected skin. Over-the-counter hydrocortisone may help. If not, doctors prescribe a corticosteroid cream. If the rash is particularly severe, a corticosteroid can be taken by mouth. If itching is severe, hydroxyzine or diphenhydramine (both antihistamines) taken by mouth can be tried.


Poison Ivy Dermatitis

About 50 to 70% of people are sensitive to the plant oil urushiol contained in poison ivy, poison oak, and poison sumac. Similar oils are also present in the shells of cashew nuts; the leaves, sap, and fruit skin of the mango; and Japanese lacquer. Once a person has been sensitized by contact with these oils, subsequent exposure causes a contact dermatitis.

The oils are quickly absorbed into the skin but may remain active on clothing, tools, and pet fur for long periods of time. Smoke from burning plants also contains the oil and may cause a reaction in certain people.

Symptoms of poison ivy dermatitis begin 8 to 48 hours after contact and consist of intense itching, a red rash, and multiple blisters, which may be tiny or very large. Typically, the blisters occur in a straight line following the track where the plant brushed along the skin. The rash may appear at different times in different locations either because of repeat contact with contaminated clothing and other objects or because some parts of the skin are more sensitive than others. The blister fluid itself is not contagious. The itching and rash last for 2 to 3 weeks.

Recognition and avoidance of contact with the plants is the best prevention. A number of commercial barrier creams and lotions can be applied before exposure to minimize, but not completely prevent, absorption of oil by the skin. The oil can soak through latex rubber gloves. Washing the skin with soap and water prevents absorption of the oil if done immediately. Stronger solvents, such as acetone, alcohol, and various commercial products, are probably no more effective. Desensitization with various shots or pills or by eating poison ivy leaves is not effective.

Treatment of poison ivy dermatitis helps relieve symptoms but does not shorten the duration of the rash. The most effective treatment is with corticosteroids. Small areas of rash are treated with strong topical corticosteroids (drugs applied to the skin), such as triamcinolone, clobetasol, or diflorasone—except on the face and genitals, where only mild corticosteroids, such as 1% hydrocortisone, should be applied. People with large areas of rash or significant facial swelling are given high-dose corticosteroids taken by mouth. Cool compresses wet with water or aluminum acetate may be used on large blistered areas. Antihistamines given by mouth may help with itching. Lotions and creams containing antihistamines are seldom used.

Drugs Mentioned In This Article

Generic Name Select Brand Names
No US brand name
NOTE: This is the Consumer Version. DOCTORS: Click here for the Professional Version
Click here for the Professional Version
Others also read

Also of Interest


Download the Manuals App iOS ANDROID
Download the Manuals App iOS ANDROID
Download the Manuals App iOS ANDROID