Hives and Rashes

Heat rash or “prickly heat” is a stinging rash that tends to appear on the neck, chest or in skin creases like those under the arm, in the groin or under the breast. When someone sweats profusely, especially in constricting clothes, it can cause tiny sweat glands in those areas to rupture. The rash (known medically as miliaria) will go away if you avoid ointments and keep the area cool and dry.

Unlike most other rashes, hives are under the skin.

“Rash” is a catch-all layman’s term, defined broadly as any inflammation in the skin. The range of common skin rashes stretches from irritations like a diaper rash to chronic skin diseases like psoriasis to painful conditions like shingles.

Hives (urticaria) result from a build-up of fluid underneath the top layer of skin. What happens is that histamine is released into blood vessels, usually triggered by an allergic reaction or by certain drugs (read your warning labels). The vessels then stretch out so much that they begin to leak fluid; and as the fluid accumulates, it causes swollen lesions called wheals which give the skin the texture of an orange peel. Wheals itch like mad.

Unless you have a chronic (ongoing) condition, hives should disappear within a day or two. In the meantime, do what you need to get comfortable. A cold compress or cold shower usually brings relief to itching; since hives are not on the skin’s surface, there’s no reason not to get the skin wet. Some rashes, however, will worsen and spread when the skin gets wet, such as a leaky, puss-oozing poison ivy blister.

Any guess as to how to block the effect of histamines? Right, take an antihistamine. Over-the-counter antihistamines like Claritin will inhibit the development of new wheals. “Patients think they need a shot, and doctors often give them, but the antihistamines actually are absorbed well orally,” says Dr. Joseph Jorizzo, a spokesperson for the American Academy of Dermatology. Once you already have a particular hive, he explains, it’s not going to go away any faster with a shot. “The treatment, really, is to prevent your getting the next crop of wheals. The antihistamine must be taken around the clock to prevent new hives.”

Though a single outbreak of hives (acute urticaria) can last a few days, each of the welt-like wheals will only be around for 24 hours, maximum. “If you take a pen and draw a circle around one of the wheals, by definition it will go away in less than 24 hours,” Jorizzo explains.  “You may get another one right next to it, but [each wheal] comes and goes within a day’s time.”

It’s rare for anxiety to cause hives.

We sometimes hear people worrying about “breaking out in hives” in response to a stressful or anxious scenario, such as a wedding day. However, such a reaction is very unlikely unless you already suffer from regular outbreaks. Barring a chronic condition, you probably won’t break out in hives unless you’re allergic to the flowers, the appetizer or your fiancée.

Hives and Rashes has been reviewed for accuracy by Dr. Joseph Jorizzo, professor, founder and former chair of the Department of Dermatology at Wake Forest University School of Medicine in Winston-Salem, N.C.

Confused by health myths and misinformation? Each week, Rich Maloof talks to leading health experts to bring you the straight facts on a broad range of health topics.

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