Defining Atopic Dermatitis

Defining Atopic Dermatitis
Source: National Institute of Arthritis and Musculoskeletal and Skin Diseases

Atopic dermatitis is a chronic (long-lasting) disease that affects the skin. The word "dermatitis" means inflammation of the skin. "Atopic" refers to a group of diseases that are hereditary (that is, run in families) and often occur together, including asthma, allergies such as hay fever, and atopic dermatitis. In atopic dermatitis, the skin becomes extremely itchy and inflamed, causing redness, swelling, cracking, weeping, crusting, and scaling. Atopic dermatitis most often affects infants and young children, but it can continue into adulthood or first show up later in life. In most cases, there are periods of time when the disease is worse, called exacerbations or flares, followed by periods when the skin improves or clears up entirely, called remissions. Many children with atopic dermatitis will experience a permanent remission of the disease when they get older, although their skin often remains dry and easily irritated. Environmental factors can bring on symptoms of atopic dermatitis at any time in the lives of individuals who have inherited the atopic disease trait.

Atopic dermatitis is often referred to as "eczema," which is a general term for the many types of dermatitis. Atopic dermatitis is the most common of the many types of eczema. Several have very similar symptoms. Types of eczema are described in the box to the right.

Atopic dermatitis is very common. It affects males and females equally and accounts for 10 to 20 percent of all referrals to dermatologists (doctors who specialize in the care and treatment of skin diseases). Atopic dermatitis occurs most often in infants and children and its onset decreases substantially with age. Scientists estimate that 65 percent of patients develop symptoms in the first year of life, and 90 percent develop symptoms before the age of 5. Onset after age 30 is less common and often occurs after exposure of skin to harsh conditions. People who live in urban areas and in climates with low humidity seem to be at an increased risk for developing atopic dermatitis.

Although it is difficult to identify exactly how many people are affected by atopic dermatitis, an estimated 10 percent of infants and young children experience symptoms of the disease. Roughly 60 percent of these infants continue to have one or more symptoms of atopic dermatitis into adulthood. This means that more than 15 million people in the United States have symptoms of the disease.

The cause of atopic dermatitis is not known, but the disease seems to result from a combination of genetic (hereditary) and environmental factors. Evidence suggests the disease is associated with other so-called atopic disorders such as hay fever and asthma, which many people with atopic dermatitis also have. In addition, many children who outgrow the symptoms of atopic dermatitis go on to develop hay fever or asthma. Although one disorder does not cause another, they may be related, thereby giving researchers clues to understanding atopic dermatitis.

In the past, doctors thought that atopic dermatitis was caused by an emotional disorder. We now know that emotional factors, such as stress, can make the condition worse, but they do not cause the disease. Also, atopic dermatitis is not contagious; it cannot be passed from one person to another.

Types of Eczema (Dermatitis) Atopic dermatitis: a chronic skin disease characterized by itchy, inflamed skin Contact eczema: a localized reaction that includes redness, itching, and burning where the skin has come into contact with an allergen (an allergy-causing substance) or with an irritant such as an acid, a cleaning agent, or other chemical Allergic contact eczema (dermatitis): a red, itchy, weepy reaction where the skin has come into contact with a substance that the immune system recognizes as foreign, such as poison ivy or certain preservatives in creams and lotions Seborrheic eczema: yellowish, oily, scaly patches of skin on the scalp, face, and occasionally other parts of the body Nummular eczema: coin-shaped patches of irritated skin—most common on the arms, back, buttocks, and lower legs—that may be crusted, scaling, and extremely itchy Neurodermatitis: scaly patches of skin on the head, lower legs, wrists, or forearms caused by a localized itch (such as an insect bite) that becomes intensely irritated when scratched Stasis dermatitis: a skin irritation on the lower legs, generally related to circulatory problems Dyshidrotic eczema: irritation of the skin on the palms of hands and soles of the feet characterized by clear, deep blisters that itch and burn

Symptoms of Atopic Dermatitis

Symptoms vary from person to person. The most common symptoms are dry, itchy skin; cracks behind the ears; and rashes on the cheeks, arms, and legs. The itchy feeling is an important factor in atopic dermatitis, because scratching and rubbing in response to itching worsen the skin inflammation characteristic of this disease. People with atopic dermatitis seem to be more sensitive to itching and feel the need to scratch longer in response. They develop what is referred to as "the itch-scratch cycle": The extreme itchiness of the skin causes the person to scratch, which in turn worsens the itch, and so on. Itching is particularly a problem during sleep, when conscious control of scratching decreases and the absence of other outside stimuli makes the itchiness more noticeable.

The way the skin is affected by atopic dermatitis can be changed by patterns of scratching and resulting skin infections. Some people with the disease develop red, scaling skin where the immune system in the skin is becoming very activated. Others develop thick and leathery skin as a result of constant scratching and rubbing. This condition is called lichenification. Still others develop papules, or small raised bumps, on their skin. When the papules are scratched, they may open (excoriations) and become crusty and infected. The box below lists common skin features of the disease. These conditions can also be found in people without atopic dermatitis or with other types of skin disorders.

Atopic dermatitis may also affect the skin around the eyes, the eyelids, and the eyebrows and lashes. Scratching and rubbing the eye area can cause the skin to change in appearance. Some people with atopic dermatitis develop an extra fold of skin under their eyes, called an atopic pleat or Dennie-Morgan fold. Other people may have hyperpigmented eyelids, meaning that the skin on their eyelids darkens from inflammation or hay fever (allergic shiners). Patchy eyebrows and eyelashes may also result from scratching or rubbing.

Researchers have noted differences in the skin of people with atopic dermatitis that may contribute to the symptoms of the disease. The epidermis, which is the outermost layer of skin, is divided into two parts: The inner part contains moist, living cells, and the outer part, known as the horny layer or stratum corneum, contains dry, flattened, dead cells. Under normal conditions the stratum corneum acts as a barrier, keeping the rest of the skin from drying out and protecting other layers of skin from damage caused by irritants and infections. When this barrier is damaged, irritants act more intensely on the skin.

The skin of a person with atopic dermatitis loses too much moisture from the epidermal layer, allowing the skin to become very dry and reducing its protective abilities. In addition, the patient’s skin is very susceptible to recurring infections, such as staphylococcal and streptococcal bacterial skin infections and warts, herpes simplex, and molluscum contagiosum (skin disorders caused by a viruses).

Skin Features of Atopic Dermatitis Lichenification: thick, leathery skin resulting from constant scratching and rubbing Papules: small raised bumps that may open when scratched, becoming crusty and infected Ichthyosis: dry, rectangular scales on the skin Keratosis pilaris: small, rough bumps, generally on the face, upper arms, and thighs Hyperlinear palms: increased number of skin creases on the palms Urticaria: hives (red, raised bumps), often after exposure to an allergen, at the beginning of flares, or after exercise or a hot bath Cheilitis: inflammation of the skin on and around the lips Atopic pleat (Dennie-Morgan fold): an extra fold of skin that develops under the eye Hyperpigmented eyelids: eyelids that have become darker in color from inflammation or hay fever