Hairs are adulterants of major regulatory significance in foods. Hairs may indicate contamination by mammals and their metabolic byproducts through direct contact by the animal with a food product or a food product contact surface; through close proximity of the animal to food products; or, occasionally, through an animal accidentally ending up as an ingredient in the product. The significance of hairs can range from incidental contaminants to indicators of gross insanitation. Hairs may be shed directly by the source animal or may have a fecal origin as a result of grooming behaviors. Mammalian hairs can often be identified to precise levels using distinctive morphological characters of individual hairs that are visible at high magnification (200X - 400X). Analysts in the microanalytical laboratory must be familiar with the micromorphology of mammalian hairs in order to accurately identify the source animal. Hair identification allows evaluation of the etiology of the contamination to determine the legal and sanitary significance of hair contaminants in food. Hair morphology, animal sources of hair contaminants, modes of contamination and regulatory significance of the various animal taxa will be discussed. Identification of fur hairs, the most frequently occurring type in food samples, will be discussed and a hair identification key will be included. Key diagnostic features and differences among the most commonly found hairs will be discussed and illustrated with photomicrographs.