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.
1 Seborrheic dermatitis, a condition which occurs as an allergic reaction to the yeast present on the skin surface, can cause yellow-colored skin rashes on the head, face, neck and even genitalia.  Skin rash in newly born babies can occur due to congential cutaneous candidiasis.