Nettles sting through hollow hairs that break on contact and release an irritating chemical into skin.

The longer version

Each stinging hair on a nettle is a tiny hollow needle with a brittle tip. Pressure from a passing hand or leg snaps the tip off, leaving a sharp point that pierces the skin and injects the fluid held inside the hair.

That fluid contains several irritant chemicals, which together produce the burning sensation and the rash that follows. The hairs point upward, so brushing against the plant in one direction breaks more of them. The whole arrangement works as a defence against grazing animals rather than an attack on anything. Related species in other regions use the same apparatus, and the effect on skin is much the same.

Where this entry sits

Plants and Trees gathers ordinary and surprising details about how green things live, from the tallest forest giants down to the moss on a garden wall. Expect notes on flowers, seeds, roots, leaves, fungi, and the quiet tricks plants use to spread and survive. The full list sits on the Plants and Trees page, where every entry is listed in order.