What is a Physical Urticaria?
People who have a physical urticaria have a physical trigger for their hives, such as pressure, heat, cold, sunlight, water, or exercise. Up to 20 to 30 percent of people with chronic urticaria (hives lasting more than 6 weeks) have a physical cause.What is Dermatographism?
Dermatographism means the ability to write on the skin. People with this form of chronic urticaria are sensitive to touch and pressure, as well as scratching. The areas of skin that are touched or scratched get a raised, red and itchy rash. While many people with chronic urticaria have some features of dermatographism, people with true dermatographism have pressure as the only trigger for their symptoms.In some forms of dermatographism, symptoms occur after within a few minutes of stroking the skin with an object (such as a pen or tongue depressor), with the rash going away without treatment within an hour. Other forms of dermatographism, such as delayed pressure urticaria, result in a burning sensation and pain that may last for hours after the pressure was applied.
It is unknown why dermatographism occurs. This is possibly a true allergy, meaning that allergic antibodies are present in the body that causes the reaction, but it is unknown what the antibodies are targeted against.
How is Dermatographism Diagnosed?
The diagnosis is made by stroking the skin with an object, such as a pen. The appearance of a red, itchy, and sometimes raised rash along the area of the pen stroke makes the diagnosis. Delayed pressure urticaria is diagnosed by placing a weight on the skin or over the shoulder (such as a heavy back pack) for a certain period of time, with an area of swelling and redness appearing for a few hours and possibly lasting for days.How is Dermatographism Treated?
If a person is not particularly bothered by dermatographism, then no treatment is needed. Symptoms can be decreased with the use of various antihistamines. Many of the antihistamines that cause sedation, including hydroxyzine, seem to work especially well.Want to keep learning? Find out about cholinergic urticaria.
Source:
Dice, JP. Physical Urticaria. Immunol Allergy Clin N Am. 2004;24:225-246.
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