The dermatitis is a common allergic skin disease in horses. It is due to hypersensitivity to certain horses saliva insects (Culicoides genus). Clinical signs are seasonal spring to autumn, the location of the lesions is primarily the back line from the neck (mane) at the base of the tail. The lesions cause a marked alopecia, pruritus, stress and loss of state. Diagnosis is made clinically by means of a scraping.