February 12, 2007

Skin Itching and Noninfectious Rashes


Itching and rashes may develop as the result of infection or irritation or from a reaction of the immune system. Some rashes occur mostly in children, whereas others almost always occur in adults. Sometimes an immune reaction is triggered by substances a person touches or eats, but many times doctors do not know why the immune system reacts to produce a skin rash.

The diagnosis of most noninfectious skin rashes is based on the appearance of the rash. The cause of a rash cannot be determined by blood tests, and tests of any kind are rarely performed. However, persistent rashes, particularly those that do not respond to treatment, may lead the doctor to perform a skin biopsy, in which a small piece of skin is surgically removed for examination under a microscope. Also, if the doctor suspects a contact allergy as the cause, skin tests may be performed.

Dermatitis (eczema) is inflammation of the upper layers of the skin, causing itching, blisters, redness, swelling, and often oozing, scabbing, and scaling.

Dermatitis is a broad term covering many different disorders that all result in a red, itchy rash. The term eczema is sometimes used for dermatitis. Some types of dermatitis affect only specific parts of the body, whereas others can occur anywhere. Some types of dermatitis have a known cause; others do not. However, dermatitis is always the skin's way of reacting to severe dryness, scratching, a substance that is causing irritation, or an allergen. Typically, that substance comes in direct contact with the skin, but sometimes the substance is swallowed. In all cases, continuous scratching and rubbing may eventually lead to thickening and hardening of the skin.

Dermatitis may be a brief reaction to a substance. In such cases it may produce symptoms, such as itching and redness, for just a few hours or a day or two. Chronic dermatitis persists over a period of time. The hands and feet are particularly vulnerable to chronic dermatitis, because the hands are in frequent contact with many foreign substances and the feet are in the warm, moist conditions created by socks and shoes that favor fungal growth.

Chronic dermatitis may represent a contact, fungal, or other dermatitis that has been inadequately diagnosed or treated, or it may be one of several chronic skin disorders of unknown origin, such as pompholyx (see Itching and Noninfectious Rashes: Pompholyx) or hyperkeratotic palmar eczema. Because chronic dermatitis produces cracks and blisters in the skin, any type of chronic dermatitis may lead to bacterial infection.

Contact Dermatitis
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) or allergic reaction (allergic contact dermatitis).

Irritant contact dermatitis occurs when a chemical substance causes direct damage to the skin. Typical irritating substances are acids, alkalis (such as drain cleaners), solvents (such as acetone in nail polish remover), and strong soaps. Some of these chemicals cause skin changes within a few minutes, whereas others require longer exposure. People vary in the sensitivity of their skin to irritants. Even very mild soaps and detergents may irritate the skin of some people after frequent or prolonged contact.

Allergic contact dermatitis is a reaction by the body's immune system to a substance contacting the skin. 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 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 (latex), antibiotics, fragrances, preservatives, and some metals (nickel, 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). Such substances include sunscreens, aftershave lotions, certain perfumes, antibiotics, coal tar, and oils.

Common Causes of Allergic Contact Dermatitis

Cosmetics: Hair-removing chemicals, nail polish, nail polish remover, deodorants, moisturizers, aftershave lotions, perfumes, sunscreens

Metal compound (in jewelry): Nickel

Plants: Poison ivy, poison oak, poison sumac, ragweed, primrose, thistle

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

Chemicals used in clothing manufacturing: Tanning agents in shoes; rubber accelerators and antioxidants in gloves, shoes, undergarments, other apparel

Symptoms and Diagnosis

Regardless of cause or type, contact dermatitis results in itching and a rash. The itching is usually severe, but 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. 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.

Determining the cause of contact dermatitis is not always easy. Most people are unaware of all the substances that touch their skin. Often, the location of the initial rash is an important clue, particularly if it 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 and a process of elimination does not pinpoint the cause, patch testing can be performed. For this test, small patches containing substances that commonly cause dermatitis are placed on the skin for 1 to 2 days to see if 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.

Prevention and Treatment

Contact dermatitis can be prevented by avoiding contact with the causative substance. If contact does occur, the material should be washed off immediately with soap and water. If circumstances risk 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 of the causative substance is not effective in preventing contact dermatitis.

Treatment 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. Residual scaling, itching, and temporary thickening of the skin may last for days or weeks.

Itching can be relieved with a number of topical or oral drugs. 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's solution) several times a day for an hour. Larger areas may be treated with short, cool tub baths with or without colloidal oatmeal. The doctor may drain fluid from large blisters, but the blister is not removed.

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 produces 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. Sensitivity to poison ivy tends to run in families.

Symptoms begin from 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 of 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 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, 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.

Atopic Dermatitis
Atopic dermatitis is chronic, itchy inflammation of the upper layers of the skin that often develops in people who have hay fever or asthma and in people who have family members with these conditions.

Atopic dermatitis is one of the most common skin diseases, affecting 15 million people in the United States. Almost 66% of people with the disorder develop it before age 1, and 90% by age 5. In half of these people, the disorder will be gone by the teenage years; in others, it is lifelong.

Doctors do not know what causes atopic dermatitis, but people with it usually have many allergic disorders, particularly asthma, hay fever, and food allergies. The relationship between the dermatitis and these disorders is not clear; atopic dermatitis is not an allergy to a particular substance. Atopic dermatitis is not contagious.

Many conditions can make atopic dermatitis worse, including emotional stress, changes in temperature or humidity, bacterial skin infections, and contact with irritating clothing (especially wool). In some infants, food allergies may provoke atopic dermatitis.


Infants may develop red, oozing, crusted rashes on the face, scalp, diaper area, hands, arms, feet, or legs. Large areas of the body may be affected. In older children and adults, the rash often occurs (and recurs) in only one or a few spots, especially on the hands, upper arms, in front of the elbows, or behind the knees.

Although the color, intensity, and location of the rash vary, the rash always itches. The itching often leads to uncontrollable scratching, triggering a cycle of itching-scratching-itching that makes the problem worse. Scratching and rubbing can also tear the skin, leaving an opening for bacteria to enter and cause infections.

In people with atopic dermatitis, infection with the herpes simplex virus, which usually affects a small area with tiny, slightly painful blisters (see Viral Infections: Herpes Simplex Virus (HSV) Infections), may produce a serious illness with widespread dermatitis, blistering, and high fever (eczema herpeticum).

Diagnosis and Treatment

A doctor makes the diagnosis based on the typical pattern of the rash and often on whether other family members have allergies.

No cure exists, but itching can be relieved with topical or oral drugs. Certain other measures can help. Avoiding contact with substances known to irritate the skin or foods that the person is sensitive to can prevent a rash. The skin should be kept moist, either with commercial moisturizers or with petroleum jelly or vegetable oil. Moisturizers are best applied after bathing, while the skin is damp. To limit the use of corticosteroids in people being treated for long periods, doctors sometimes replace the corticosteroids with petroleum jelly for a week or more at a time. Corticosteroid tablets are a last resort for people with stubborn cases.

Phototherapy (exposure to ultraviolet light) often helps adults. This treatment is rarely recommended for children because of its potential long-term side effects, including skin cancer and cataracts.

For severe cases, the immune system can be suppressed with cyclosporine taken by mouth or tacrolimus used as an ointment. Zafirlukast, a new oral drug used to prevent asthma attacks, may also be helpful in treating atopic dermatitis.

Seborrheic Dermatitis
Seborrheic dermatitis is chronic inflammation of unknown cause that causes scales on the scalp and face and occasionally on other areas.

Seborrheic dermatitis occurs most often in infants, usually within the first 3 months of life, and between the ages of 30 and 70. The disorder is more common in men, often runs in families, and is worse in cold weather. A form of seborrheic dermatitis also occurs in as many as 85% of people with AIDS.


Seborrheic dermatitis usually begins gradually, causing dry or greasy scaling of the scalp (dandruff), sometimes with itching but without hair loss. In more severe cases, yellowish to reddish scaly pimples appear along the hairline, behind the ears, in the ear canal, on the eyebrows, on the bridge of the nose, around the nose, on the chest, and on the upper back. In infants younger than 1 month of age, seborrheic dermatitis may produce a thick, yellow, crusted scalp rash (cradle cap) and sometimes yellow scaling behind the ears and red pimples on the face. Frequently, a stubborn diaper rash accompanies the scalp rash. Older children and adults may develop a thick, tenacious, scaly rash with large flakes of skin.


The scalp can be treated with a shampoo containing pyrithione zinc, selenium sulfide, an antifungal drug, salicylic acid and sulfur, or tar. The person usually uses the medicated shampoo every other day until the dermatitis is controlled and then twice weekly. Ketoconazole cream is often effective as well. In adults, thick crusts and scales, if present, can be loosened with overnight application of corticosteroids or salicylic acid under a shower cap.

Often, treatment must be continued for many weeks; if the dermatitis returns after the treatment is discontinued, treatment can be restarted. Topical corticosteroids are also used on the head and other affected areas. On the face, only mild corticosteroids, such as 1% hydrocortisone, should be used. Even mild corticosteroids must be used cautiously, because long-term use can thin the skin and cause other problems.

In infants and young children who have a thick scaly rash on the scalp, salicylic acid in mineral oil can be rubbed gently into the rash with a soft toothbrush at bedtime. The scalp can also be shampooed daily with mild baby shampoo, and 1% hydrocortisone cream can be rubbed into the scalp.

Nummular Dermatitis

Nummular dermatitis is a persistent, usually itchy, rash and inflammation characterized by coin-shaped spots with tiny blisters, scabs, and scales.

The cause is unknown. Nummular dermatitis usually affects middle-aged people, occurs along with dry skin, and is most common in winter. However, the rash may come and go without any apparent reason.

The round spots start as itchy patches of pimples and blisters that later ooze and form crusts. The rash may be widespread. Often, spots are more obvious on the backs of the arms or legs and on the buttocks, but they also appear on the torso.

Most people benefit from skin moisturizers. Other treatments include antibiotics taken by mouth, corticosteroid creams and injections, and phototherapy (exposure to ultraviolet light). All treatments, however, are often unsatisfactory.

Generalized Exfoliative Dermatitis

Generalized exfoliative dermatitis (erythroderma) is severe inflammation that causes the entire skin surface to become red, cracked, and covered with scales.

Certain drugs (especially penicillins, sulfonamides, isoniazid, phenytoin, and barbiturates) may cause this disorder. In some cases, it is a complication of other skin diseases, such as atopic dermatitis, psoriasis, and contact dermatitis. Certain lymphomas (cancers of the lymph nodes (see Lymphomas: Introduction) may also cause generalized exfoliative dermatitis. In many cases, the cause is unknown.

Symptoms and Diagnosis

Exfoliative dermatitis may start rapidly or slowly. At first the entire skin surface becomes red and shiny. Then the skin becomes scaly, thickened, and sometimes crusted. Sometimes the hair and nails fall out. Some people have itching and swollen lymph nodes. Although many people have a fever, they may feel cold because so much heat is lost through the damaged skin. Large amounts of fluid and protein may seep out, and the damaged skin is a poor barrier against infection.

Because symptoms of exfoliative dermatitis are similar to those of skin infection, doctors send samples of skin and blood to the laboratory to exclude infection as a cause.


Early diagnosis and treatment are important in preventing infection from developing in the affected skin and in keeping fluid and protein loss from becoming life threatening.

People with severe exfoliative dermatitis often need to be hospitalized and given antibiotics (for infection), intravenous fluids (to replace the fluids lost through the skin), and nutritional supplements. Care may include the use of drugs and heated blankets to control body temperature. Cool baths followed by applications of petroleum jelly and gauze may help protect the skin. Corticosteroids (such as prednisone) given by mouth or intravenously are used only when other measures are unsuccessful or the disease worsens. Any drug or chemical that could be causing the dermatitis should be eliminated. If lymphoma is causing the dermatitis, treatment of the lymphoma is helpful.

Stasis Dermatitis
Stasis dermatitis is inflammation on the lower legs from pooling of blood and fluid.

Stasis dermatitis tends to occur in people who have varicose (dilated, twisted) veins (see Venous Disorders: Varicose Veins) and swelling (edema). It usually occurs on the ankles but may spread upward to the knees. At first, the skin becomes reddened and mildly scaly. Over several weeks or months, the skin turns dark brown. Eventually, areas of the skin may break down and form an open sore (ulcer), typically near the ankle. Ulcers sometimes become infected with bacteria. Stasis dermatitis makes the legs feel itchy and swollen, but not painful. Ulcers are usually painful.


Long-term treatment is aimed at keeping blood from pooling in the veins around the ankles. When sitting, the person should elevate the legs above the level of the heart. Properly fitted prescription support hose (compression stockings) also prevent pooling of blood and decrease swelling. Department store "support" stockings are not adequate.

For dermatitis of recent onset, soothing compresses, such as gauze pads soaked in tap water or aluminum acetate (Burow's solution), may make the skin feel better and can help prevent infection by keeping the skin clean. If the disorder worsens, as evidenced by increased warmth, redness, small ulcers, or pus, a more absorbent dressing can be used. Corticosteroid creams are also helpful and are often combined with zinc oxide paste and applied in a thin layer. Corticosteroids should not be applied directly to an ulcer because this will interfere with healing.

When a person has large or extensive ulcers, special moisture-containing hydrocolloid or hydrogel dressings may be used. Antibiotics are used only when the skin is already infected. Sometimes, skin from elsewhere on the body may be grafted to cover very large ulcers.

Some people may need an Unna's boot, which is a woven stretch wrap filled with a gelatin paste that contains zinc. The wrap is applied to the ankle and lower leg where it hardens, similar to but softer than a cast. The boot limits swelling and helps protect the skin from irritation, and the paste helps heal the skin. At first the boot is changed every 2 or 3 days, but later it is left on for a week at a time.

In stasis dermatitis, the skin is easily irritated; antibiotic creams, first-aid (anesthetic) creams, alcohol, witch hazel, lanolin, or other chemicals should not be used because they can make the disorder worse.

Localized Scratch Dermatitis

Localized scratch dermatitis (lichen simplex chronicus, neurodermatitis) is chronic, itchy inflammation of the top layer of the skin.

Localized scratch dermatitis is caused by chronic scratching of an area of skin. The act of scratching triggers more itching, beginning a vicious circle of itching-scratching-itching. Sometimes the scratching begins for no apparent reason. Other times scratching starts because of a contact dermatitis, parasitic infestation, or other condition, but the person continues to scratch long after the inciting cause is gone. Doctors do not know why this happens, but psychologic factors may play a role. The disorder does not seem to be allergic. More women than men have localized scratch dermatitis, and it is common among Asians and Native Americans. It usually develops between the ages of 20 and 50.

Symptoms and Diagnosis

Localized scratch dermatitis can occur anywhere on the body, including the anus (pruritus ani and the vagina (pruritus vulvae, but is most common on the head, arms, and legs. In the early stages, the skin looks normal, but it itches. Later, dryness, scaling, and dark patches develop as a result of the scratching and rubbing.

Doctors try to discover any possible underlying allergies or diseases that may be causing the initial itching. When the disorder occurs around the anus or vagina, the doctor may investigate the possibility of pinworms, trichomoniasis, hemorrhoids, local discharges, fungal infections, warts, contact dermatitis, or psoriasis as the cause.


For the disorder to clear up, the person must stop all scratching and rubbing of the area. Standard treatments for itching should be followed (see Itching and Noninfectious Rashes: Treatment). Using surgical tape saturated with a corticosteroid helps relieve itching and inflammation and protects the skin from scratching. The doctor may inject longer-acting corticosteroids under the skin to control the itching.

When this disorder develops around the anus or vagina, the best treatment is a corticosteroid cream. Zinc oxide paste may be applied over the cream to protect the area; the paste can be removed with mineral oil.

Perioral Dermatitis

Perioral dermatitis is a red, bumpy rash around the mouth and on the chin.

The disorder, whose cause is unknown, mainly affects women between the ages of 20 and 60.

Treatment is with tetracyclines or other antibiotics taken by mouth. If these antibiotics do not clear up the rash and the disorder is particularly severe, isotretinoin, an acne drug, may help. Corticosteroids and some oily cosmetics, especially moisturizers, tend to worsen the disorder.

Pompholyx is a chronic dermatitis characterized by itchy blisters on the palms and sides of the fingers and sometimes on the soles of the feet.

Pompholyx is sometimes called dyshidrosis, which means "abnormal sweating," but the disorder has nothing to do with sweating. Doctors do not know what causes pompholyx, but stress may be a factor as well as some ingested substances such as nickel, chromium, and cobalt. It is more common in adolescents and young adults.

The blisters are often scaly, red, and oozing. Pompholyx comes and goes in attacks that last 2 to 3 weeks. Pompholyx takes weeks to go away on its own. Wet compresses with potassium permanganate or aluminum acetate (Burow's solution) may help the blisters resolve. Strong topical corticosteroids may help itching and inflammation.

Adapted from Merck & Co., Inc.