Sweet Itch Remedies for horses and the owners who love them. Sweet itch is caused by an allergic reaction to the protein in the saliva of biting flies, mosquitoes and other insects.  This causes the immune system to attack its own cells and leads to an extreme reaction that causes the loss of hair and intense itching as the horse tries to relieve the discomfort. Make sure you have information on affordable, effective products to relieve Sweet Itch today.