Researchers supported by the National Institute of Arthritis and Musculoskeletal and Skin Diseases and other institutes of the National Institutes of Health are gaining a better understanding of what causes atopic dermatitis and how it can be managed, treated, and, ultimately, prevented. Some promising avenues of research are described below.

Genetics: Although atopic dermatitis runs in families, the role of genetics (inheritance) remains unclear. It does appear that more than one gene is involved in the disease.

Research has helped shed light on the way atopic dermatitis is inherited. Studies show that children are at increased risk for developing the disorder if there is a family history of other atopic disease, such as hay fever or asthma. The risk is significantly higher if both parents have an atopic disease. In addition, studies of identical twins, who have the same genes, show that in an estimated 80 to 90 percent of cases, atopic disease appears in both twins. Fraternal (nonidentical) twins, who have only some genes in common, are no more likely than two other people in the general population to both have an atopic disease. These findings suggest that genes play an important role in determining who gets the disease.

Biochemical Abnormalities: Scientists suspect that changes in the skin’s protective barrier make people with atopic dermatitis more sensitive to irritants. Such people have lower levels of fatty acids (substances that provide moisture and elasticity) in their skin, which causes dryness and reduces the skin’s ability to control inflammation.

Other research points to a possible defect in a type of white blood cell called a monocyte. In people with atopic dermatitis, monocytes appear to play a role in the decreased production of an immune system hormone called interferon gamma (IFN-γ), which helps regulate allergic reactions. This defect may cause exaggerated immune and inflammatory responses in the blood and tissues of people with atopic dermatitis.

Faulty Regulation of Immunoglobulin E (IgE): As already described in the section on diagnosis, IgE is a type of antibody that controls the immune system’s allergic response. An antibody is a special protein produced by the immune system that recognizes and helps fight and destroy viruses, bacteria, and other foreign substances that invade the body. Normally, IgE is present in very small amounts, but levels are high in 80 to 90 percent of people with atopic dermatitis.

In allergic diseases, IgE antibodies are produced in response to different allergens. When an allergen comes into contact with IgE on specialized immune cells, the cells release various chemicals, including histamine. These chemicals cause the symptoms of an allergic reaction, such as wheezing, sneezing, runny eyes, and itching.

The release of histamine and other chemicals alone cannot explain the typical long-term symptoms of the disease. Research is underway to identify factors that may explain why too much IgE is produced and how it plays a role in the disease.

Immune System Imbalance: Researchers also think that an imbalance in the immune system may contribute to the atopic dermatitis. It appears that the development of part of the immune system responsible for stimulating IgE is overactive, and the part that handles skin viral and fungal infections is underactive. Indeed, the skin of people with atopic dermatitis shows increased susceptibility to skin infections. This imbalance appears to result in the skin’s inability to prevent inflammation, even in areas of skin that appear normal. In one project, scientists are studying the role of the infectious bacterium Staphylococcus aureus (S. aureus) in atopic dermatitis.

Researchers believe that one type of immune cell in the skin, called a Langerhans cell, may be involved in atopic dermatitis. Langerhans cells pick up viruses, bacteria, allergens, and other foreign substances that invade the body and deliver them to other cells in the immune defense system. Langerhans cells appear to be hyperactive in the skin of people with atopic diseases. Certain Langerhans cells are particularly potent at activating white blood cells called T cells in atopic skin, which produce proteins that promote allergic response. This function results in an exaggerated response of the skin to tiny amounts of allergens.

Scientists have also developed mouse models to study step-by-step changes in the immune system in atopic dermatitis, which may eventually lead to a treatment that effectively targets the immune system.

Drug Research: Some researchers are focusing on new treatments for atopic dermatitis, including biologic agents, fatty acid supplements, and new forms of phototherapy.

For example, they are studying how ultraviolet light affects the skin’s immune system in healthy and diseased skin. They are also investigating biologic agents, including several aimed at modifying the response of the immune system. A biologic agent is a new type of drug based on molecules that occur naturally in the body. One promising treatment is the use of thymopentin to reestablish balance in the immune system.

Researchers also continue to look for drugs that suppress the immune system. In this regard, they are studying the effectiveness of cyclosporine A. Clinical trials are underway with another drug called FK506, which is applied to the skin rather than taken orally. Also, antiinflammatory drugs have been developed that affect multiple cells and cell functions, and may prove to be an effective alternative to corticosteroids in the treatment of atopic dermatitis.

Several experimental treatments are being evaluated that attempt to replace substances that are deficient in people with atopic dermatitis. Evening primrose oil is a substance rich in gamma-linolenic acid, one of the fatty acids that is decreased in the skin of people with atopic dermatitis. Studies to date using evening primrose oil have yielded contradictory results. In addition, dietary fatty acid supplements have not proven highly effective. There is also a great deal of interest in the use of Chinese herbs and herbal teas to treat the disease. Studies to date show some benefit, but not without concerns about toxicity and the risks involved in suppressing the immune system without close medical supervision.