Thehorse.com - Full Article
By Susan L. White, DVM, MS, Dipl. ACVIM Aug 1, 2000
Skin problems in horses are some of the most frustrating disorders to manage for both owner and veterinarian. Skin problems can disfigure a horse, and even can cause unsoundness. In addition, many skin diseases, such as allergies, have a complex cause so that one easy treatment is not available.
Signs of allergies in many horses appear with the arrival of summer and become progressively worse each year. Often horses with this history are allergic to insect bites (insect hypersensitivity). Several different clinical syndromes have been associated with insect hypersensitivity, such as Queensland or sweet itch, which is caused by Culicoides species (no-see-ums). However, any biting insect can be involved in insect hypersensitivity. In fact, many affected horses are allergic to the bites of more than one kind of insect.
The first signs can include redness and large, flat, circular swellings (wheals) or raised nodules with or without crusting. Intense itching (pruritus) often leads to skin damage, hair loss, secondary infections, and thickened, wrinkled skin...
Read more here: