The Human Scratch-Pad

Some people have skins so sensitive that it is possible to write on them with a fingernail or the smoothly curved end of a paper clip. This extreme sensitivity, called dermographia ("writing on the skin") is the usual explanation when patients complain that they are "allergic to everything," two Little Rock physicians reported in the A.M.A. Journal. Although the condition has been known for years, it is often overlooked and causes a lot of needless doctoring.

Patients of this type, say Allergists Thomas G. Johnston and Alan G. Cazort, react simply to pressure on the skin. When the allergist applies a patch containing a suspected cause of allergic reaction, the patient reacts all right--but to the pressure of the patch, not to the supposedly allergenic substance. In their practice the doctors found that many patients who say they are allergic to wool are actually irritated by the wool's rough fibers: properly conducted patch tests show that they do not react to pure wool, or the wool in their particular sweaters. For girls, wearing a cotton blouse under the wool sweater usually solves the problem.

In children, the skin frequently shows wheals if stroked repeatedly in the same spot, but this sensitivity usually wears off. Among adults, dermographia may occur in either sex and show up as redness and swelling around the belt or girdle line, or under shoulder straps or suspenders. Antihistamines are generally effective in controlling the reaction, say the Little Rock doctors.

There is a simple way to weed out patients who are "allergic to everything": apply two patches with equal pressure, one patch containing suspected allergen and the other inert. If the reaction is the same, the patient has dermographia.

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