Pruritus is the sensation of itch that compels a horse to rub, bite, scratch, or roll against fixed objects. It is not a disease but a clinical sign of an underlying process that irritates cutaneous nerve endings in the skin and triggers the scratch reflex.
In horses the most frequent cause is insect hypersensitivity, particularly to the bites of Culicoides midges. This allergic dermatitis, widely called sweet itch or summer eczema, produces intense pruritus along the mane, tail head, and ventral midline and is the single most common pruritic condition in equine practice worldwide. Other insect sources include lice (pediculosis), stable flies, horn flies, and black flies, each tending toward characteristic distribution patterns on the body.
Ectoparasites beyond insects also produce pruritus. Chorioptic mange mites cause itching of the lower limbs, especially in heavy-feathered breeds. Sarcoptic and psoroptic mites, though less common, affect the head, neck, or body and provoke severe scratching.
Dermatophytosis (ringworm) is variably pruritic; some horses rub the affected patches while others show no itch at all. Contact dermatitis from tack, topical products, or bedding materials can localize pruritus to the area of exposure. Atopic dermatitis and food hypersensitivity are recognized in horses but diagnosed far less frequently than in small animals.
The horse’s response to persistent pruritus, including rubbing against fence posts, stall walls, or trees and biting at flanks or legs, causes secondary damage: broken mane and tail hairs, alopecia, excoriation, and open wounds vulnerable to infection. The distribution and seasonality of the itch are the two most useful diagnostic clues. Mane-and-tail pruritus worst in warm months points to Culicoides hypersensitivity; lower-leg pruritus in winter suggests chorioptic mange; generalized pruritus year-round raises suspicion of lice or systemic allergy.