Hairs

The hairs are keratinized epidermal structures originating from hair follicle located in the dermis or hypodermis. They are a defining feature of mammals and play a variety of roles depending on species and anatomical location.

Each hair consists of:

• the hair shaft, the visible, keratinized part above the skin;

• the hair root, the embedded part within the follicle;

• the hair bulb, the enlarged base where active cell division occurs;

• the hair papilla, the connective tissue at the base of the bulb containing capillaries and nerves.

The hair is contained in the hair follicle, a tubular invagination of the epidermis extending into the dermis. Associated with, sebaceous glands, arrector pili muscles, and sometimes apocrine sweat glands.

Depending on species and body region, hair is categorized as:

• Primary (guard) hairs: long, stiff, and straight; form the outer coat.

• Secondary (wool) hairs: soft and fine; contribute to undercoat insulation.

• Tactile hairs (vibrissae): sensory hairs located on the face (e.g., whiskers), richly innervated.