Definition: Technically known as equine insect hypersensitivity (EIH), sweet itch is an allergic reaction to the saliva of biting insects, most often the Culicoides species of midges and gnats. Signs: intense itchiness, wheals and swelling, primarily on the neck (under the mane), face, shoulders, withers, belly and rump (over the tail). The skin may be rubbed until it is crusty, weepy, raw and hairless. Location of the lesions may depend on the specific species of gnat; most prefer to bite on the neck and along the topline, but some target the chest, belly, tail and groin. Diagnosis: Skin scrapings and cultures may be needed to distinguish EIH from other causes of itchy dermatitis, such as mites, lice and fungal infections. Treatment: Antihistamines or corticosteroids may help ease the itch and inflammation, providing relief to the itchy y horse; antibiotics or antimicrobial shampoos can help prevent secondary infections. Pentoxifylline can be used to decrease skin reactivity, and in some cases allergy serum is worth trying.