Boar Bristle

Chemically this is hair: keratin, the same protein as your own, with nothing to leach into a mouth or onto skin. The practical concern is moisture, not chemistry. Natural bristle is porous and holds water, so a boar toothbrush or shaving brush left in a closed cup stays damp and supports bacterial growth in a way a nylon brush does not - rinse it, shake it out, and stand it bristles-down in open air. On sourcing, boar bristle is a byproduct of pork production and traceability is poor; very few brands can say which farms it came from or under what conditions, so a shopper who cares about welfare is largely being asked to take it on trust. It is not vegan.

Keratin chars rather than melting, so bristle will never deposit molten plastic on anything - but heat is still how boar brushes die. Boiling water and dishwasher cycles soften and permanently splay the bristle and swell a wooden head, which loosens the tufts. Wash in warm water at most, and keep natural-bristle brushes out of dishwashers and dryers entirely.

Boar and nylon blends are extremely common and rarely advertised, so check rather than trust. In good light or under a magnifier, real bristle varies in color and diameter within a single tuft and its tips taper and often split like hair, while nylon is uniform in diameter and color and ends bluntly or in a polished round tip; any brush with molded ball-tipped pins has nylon pins by definition, because a ball tip cannot be grown. Wet a few bristles - boar absorbs water and goes noticeably softer, nylon does not change at all. For certainty, pull one bristle and touch a flame to it: keratin smolders, smells like burning hair and leaves an ash you can crush, while nylon shrinks away, melts into a hard bead and smells like plastic. Ask a brand what percentage of the filling is boar and what anchors the tufts, since many otherwise plastic-free brushes staple them in with metal or set them in epoxy.

Rinse after use, shake the water out and dry bristles-down, and do not soak a wooden head. Comb shed hair out of a hairbrush rather than letting it mat at the base. Store brushes clean and sealed if they are going away for a season, because clothes moth larvae eat animal bristle in brushes exactly as they eat wool. A boar toothbrush is a few months; a well-kept boar hairbrush or shaving brush runs a decade or more.

The bristle itself is keratin and composts slowly, the way hair does. The brush usually does not - tufts are typically anchored with metal staples or glue in a wooden head, so the honest route is to cut or pull the tufts out for the compost and bin the staples. A brush whose bristles turn out to be nylon composts nothing at all, which is the other reason the identification above matters.