Large welts result from an allergic reaction to an internal source like food or some external factor, such as an insect bite. They appear as large red itchy bumps on the skin. The natural response by the body to cope with allergies is the release of histamine, which causes the large welts.
Urticaria, or hives, is the appearance of those large red itchy welts on the skin. Hives break down into two classifications according to the Colorado Springs Allergy and Asthma Clinic; acute and chronic. Acute hives last from one day to six weeks and then disappear. If they last more than six weeks they are chronic. Chronic hives last up to years at a time. Hives tend to appear in bunches. Scientists do not know for sure the causes of chronic urticaria. It is linked to histamine release and sometimes to allergies
Angioedema refers to a condition like hives that results in large welts around the facial area, especially the lips and eyes. It also occurs on the feet, hands and throat, according to MedlinePlus. Angioderma, like hives, results from the release of histamines by the body in response to a trigger. The definition of a trigger is a substance like pollen, animal hair, certain foods or medications that cause the body to respond with histamine.
Dermatographism is a condition caused by lightly scratching the skin. The result is the formation of large welts and lines across the area scratched. Once again the body releases histamines in response to the scratching, according to the University of Maryland Medical Center. The capillaries, or small blood vessels, under the skin dilate, which causes the appearance of the welts.
Insects like hornets, wasps, bumblebees and yellow jackets possess the ability to inject toxins into the body of their victims. For humans, this means the possibility of an allergic reaction with the appearance of large welts. The welts usually disappear within three to seven days without treatment. Treatments include antihistamines to negate the body's natural histamines.