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10 most bizarre allergies

Jan. 17, 2011, 11:05 a.m.
hives on arm from allergic reaction

Photo: andy_carter/Flickr

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Heat

Just as you can be allergic to cold, you can also be allergic to heat. People with heat urticaria develop itchy, red, swollen skin and welts when they’re exposed to temperatures above 109.4 degrees Fahrenheit. These reactions typically occur from an increase in body heat brought on by exercise, hot showers, saunas, blankets or even spicy foods.