bristle

A bristle is a stiff filament that projects from a surface. The term is used for natural hair on animals, small projections on plants, and synthetic filaments used in brushes and related tools.

In animals, bristles can be ordinary hairs produced by hair follicles or specialized tactile bristles such as vibrissae (whiskers), which help sense the surroundings. In plants, bristles are often a type of trichome—hair-like structures that can deter herbivores, reduce water loss, or reflect intense light. Bristles vary in length, stiffness, and density depending on species and function.

In industry, bristles are manufactured as filaments for brushes, toothbrushes, paint applicators, cleaning tools, and textiles. Natural bristles, such as hog or boar hair, are valued for certain textures and porosity, though synthetic options like nylon and polyester are common for hygiene and durability. The performance of a bristle set depends on material, diameter, tip shape, and arrangement (tufts, stiffness). Bristles wear with use and may shed, requiring replacement.

As a verb, bristle means to become stiff with anger or to stand up on end. In biology, hairs on the body can bristle upright in response to stimuli as part of defense or sensory adaptation.