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.
This is what causes the hives to appear on your skin, however, more specifically, viral hives are generally caused by a viral infection such as the flu, hepatitis, herpes, croup and many other viral infections. Your immune system is attempting to eradicate these viruses by releasing the histamine that causes your viral hives.