Pêlos

Pêlo, in Portuguese, refers to the filamentous projection that grows from the skin of most mammals. Pêlos are produced by hair follicles, tiny invaginations of the epidermis that extend into the dermis. Each hair consists of a shaft that emerges above the surface and a root embedded in the follicle. Melanin-containing melanocytes at the base give hair its color, and pêlo covers a range of thicknesses from fine vellus hairs to thicker terminal hairs.

Hair growth occurs in cycles: anagen (growth), catagen (transitional), and telogen (rest). The length of the anagen phase largely determines hair length. The arrector pili muscle, attached to the follicle, can raise pêlos in response to cold, fear, or touch, causing piloerection. Sebaceous glands associated with follicles secrete sebum that helps condition the hair and skin.

In humans, pêlos vary by region: vellus hairs are fine and short on most of the body, while terminal hairs are longer and darker on the scalp, eyebrows, armpits, pubic region, and some facial areas. Among other mammals, pelage can be dense, patterned, or specialized for insulation or camouflage.

Functions of pêlos include protection against friction, regulation of body temperature, and sensory input through hair follicle nerve endings. Hormonal and genetic factors influence hair growth and distribution. Abnormal patterns can indicate medical conditions such as hirsutism (excessive hair growth in androgen-sensitive areas) or alopecia (hair loss).

Etymology: pêlo derives from Latin pilus. In zoological and medical contexts, pêlos describe body hair in humans and other mammals; in everyday Portuguese, pêlos commonly refer to body hair collectively.