Sudden Cold Spell a Danger to Some : Health: A rapid drop in temperature can bring on painful, itchy rashes. Some sufferers wheeze and faint.

Many of us dread December, flinch at snowflakes and cower from the cold. But for some, the cold may be more than a matter of personal discomfort. It may be a deadly threat.

For a small group of people, perhaps less than 1% of the population, a rapid drop in temperature can cause an allergic reaction, said Dr. Martin D. Valentine of the Johns Hopkins Asthma and Allergy Center in Baltimore.

Some people develop painful, itchy rashes. In severe cases, sufferers wheeze, faint, or experience a swelling of the windpipe. For all sufferers, there is discomfort. For swimmers, the sudden shock of cold water can be fatal.

“It’s not the absolute temperature, it’s the temperature change,” Valentine said. A drop from the balmy 70s inside your home to 20 or 30 degrees just outside the front door can raise welts. A dive into a cold pool or the ocean can be much worse for allergic swimmers.

“They can go into shock and drown,” Valentine said. “It’s not a very good allergy to have.” He said it is likely that a number of unexplained drownings each year are due to swimmers who go into shock as a result of their allergy.

The symptoms are caused by the body’s overproduction of histamines.

To test for the allergy, he said, hold an ice cube against the skin. Anyone with the condition will get an itchy welt, resembling a mosquito bite and rising one-fourth inch or more above the skin.

“Most people would get some redness and irritation, but not itching and a raised welt,” he said.

One patient of Valentine’s took a dip in the ocean in the springtime, started to go into shock, staggered back on the beach and collapsed, unconscious. He was treated and survived. Another patient was so sensitive to temperature changes that he couldn’t roll down the window of his stifling hot car in the summer because the cooling breeze would trigger his allergy.

The condition can usually be controlled with specific antihistamines, Valentine said, and most physicians are familiar with the rare malady. But no one knows what causes it. Some sufferers develop a sensitivity to temperature drops after experiencing an acute allergic reaction to a bee sting or penicillin, or after they develop certain viral illnesses, such as infectious mononucleosis.

In experiments, blood from cold-allergic patients has been injected into non-allergic people. The non-allergic people usually then become cold-sensitive where the blood was injected. Valentine said that it shows that an antibody in the blood is probably responsible for the condition, at least in most cases.

“Usually this is something that affects the body universally, and not just a part of the body,” he said.

But the ailment does not always follow this pattern. Valentine recalled one cold-allergic patient who, when she went jogging in cold weather, began to swell only in her left knee. “It was not the joint, it was simply the skin over the top of the knee,” he said.