Contact dermatitis is skin inflammation caused by direct contact with a particular substance. The rash may be itchy, is confined to a specific area, and often has clearly defined boundaries.
Contact dermatitis is caused by either an irritant or an allergic reaction.
A rash develops and may be itchy or painful or both.
Doctors base the diagnosis on the appearance of the rash and a history of substances a person may have been exposed to.
People should avoid or protect themselves from substances that cause the dermatitis.
Treatment includes removing the substance that is causing the dermatitis, taking measures to relieve itching, applying corticosteroids to the skin, and sometimes applying dressings.
(See also Overview of Dermatitis.)
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 most cases of contact dermatitis, occurs when a toxic or chemical substance comes in contact with the skin and causes direct damage to the skin. Irritant contact dermatitis can be more painful than itchy.
Irritating substances include
Acids
Alkalis (such as drain cleaners)
Solvents (such as acetone in nail polish remover)
Strong soaps and detergents
Plants (such as poinsettias and peppers)
Constant moisture from body fluids (such as urine and saliva)
Some of these substances are extremely irritating and cause skin changes within a few minutes, whereas others are less irritating or 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.
People may also develop dermatitis from many of the materials they touch while at work (occupational dermatitis). It can occur immediately after an exposure or it can take a long time and repeated exposures to occur.
Sometimes irritant contact dermatitis results only after a person touches certain substances or ingests them and then exposes the skin to sunlight (phototoxic contact dermatitis—see Chemical photosensitivity). Regardless of whether the substance was touched or ingested, the rash develops only on the skin exposed to sunlight. Such substances include
Certain antibiotics when taken by mouth
Certain antihypertensives (blood pressure medications)/diuretics when taken by mouth
Certain perfumes
Nonsteroidal anti-inflammatory drugs (NSAIDs) taken by mouth
Some plants
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, 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
Metals (such as nickel)
Preservatives
Plants (such as poison ivy)
Rubber (including latex)
Fragrances
Nickel sulfate is the most common contact allergen in most populations. It is 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.
Sometimes allergic contact dermatitis results only after a person touches certain substances or ingests them and then exposes the skin to sunlight (photoallergic contact dermatitis—see Chemical photosensitivity). With photoallergic dermatitis, the reaction may spread to areas of skin that were not exposed to the sun. Typical causes include fragrances (such as musk ambrette and sandalwood), antiseptics, NSAIDs, and sunscreens.
Symptoms of Contact Dermatitis
Regardless of cause or type, contact dermatitis results in itching and a rash.
Irritant contact dermatitis causes more pain than itching. The symptoms typically decrease in intensity after 1 or 2 days once there is no more exposure to the irritating substance.
Allergic contact dermatitis usually causes more itching than pain. Symptoms may take a day or more to become noticeable and increase in intensity for 2 to 3 days after exposure.
For both, the rash varies from a mild, short-lived redness to severe swelling and large blisters. The rash develops only in areas that come in contact with the substance. However, the rash appears earlier in thin, sensitive areas of skin, such as in between the fingers, and later in areas of thicker skin or on skin that had less contact with the substance. On the hands and feet, the rash may contain tiny blisters.
The rash in allergic contact dermatitis 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.
Diagnosis of Contact Dermatitis
A doctor's evaluation and the person's history
Sometimes patch testing
Determining the cause of contact dermatitis is not always easy. The person's occupation, hobbies, household duties, travel, clothing, use of products 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.
If a doctor suspects contact dermatitis but the cause is not apparent, patch testing can be done to help identify the substance (allergen) that is causing the allergic reaction. For this test, small patches containing standard contact allergens are placed on the skin of the upper back and left on for 48 hours to see whether a rash develops beneath one of them. After 48 hours, they are removed, and the doctor evaluates the skin underneath. The skin is evaluated again a day or two later.
Prevention of Contact Dermatitis
Contact dermatitis can be prevented by avoiding contact with the substances that cause dermatitis. 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.
People who have phototoxic or photoallergic contact dermatitis should avoid exposure to sun.
Barrier creams are also available that can block certain substances, such as poison ivy and epoxy resins, from coming in contact with the skin.
Desensitization with injections or tablets that contain the causative substance is not effective in preventing contact dermatitis.
Treatment of Contact Dermatitis
Avoiding contact with the substance causing the problem
Measures to relieve itching
Corticosteroids and 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 with time. Blisters may continue to ooze and form crusts, but they soon dry. Scaling, itching, and thickening of the skin may last for days or weeks.
Prognosis for Contact Dermatitis
Allergic contact dermatitis may take several weeks to resolve after people are no longer exposed to the allergen. Irritant contact dermatitis usually resolves faster. Once people react to a substance, they usually react for the rest of their life.
People who have photoallergic contact dermatitis may continue to have flare-ups for years when exposed to the sun (called a persistent light reaction), but this is rare.
