Urticaria occurs when the body reacts to an allergen and releases histamine and other chemicals from under the surface of the skin. The histamine and chemicals cause inflammation and fluid to accumulate under the skin, causing wheals.

What does skin wheal mean?

: a suddenly formed elevation of the skin surface : welt especially : a flat burning or itching eminence on the skin.

What does Wheals look like?

Wheal: A raised, itchy (pruritic) area of skin that is sometimes an overt sign of allergy. Not all wheals are alike. They may be redder or paler than the skin around them. They may vary in configuration and may be rounded or flat-topped.