What Causes Itchy Body Welts?

esthAlto/Frederic Cirou/PhotoAlto Agency RF Collections/Getty Images

Itchy body welts, also referred to as hives, appear in response to histamine, a chemical that is released by mast cells, which are its major source, according to Dermatopedia from the Dermatological Society of New Jersey. When the cells release the chemical, itching and welts are experienced almost immediately.