Indusium: the case made by an insect larva: a membranous layer of the embryo of Locustidae below the serosa. Explanation of Terms Used in Entomology John. B. Smith. serosa: the outer membrane that envelops the forming embryo, the amnion and the remainder of the egg. Explanation of Terms Used in Entomology John.
In essence, your body forms an allergic reaction to stress. Unfortunately, stress can not be eliminated with histamine, so instead, the histamine just causes hives to appear on your face, neck, chest and other parts of your body.
Hives and swelling triggered by a physical stimulus to the skin are known as physical urticaria. It is thought that physical stimulation (light, heat, cold, pressure) leads to a change in local IgE that then stimulates mast cells to liberate mediators that cause the itching and hives.