Why do nettles sting?

Answer 1

Nettles (Urtica dioica) sting to protect themselves, the question that you should be asking is How do nettles sting? Well, now you asked... The stinging structure of the nettle is very similar to the hypodermic needle although it predates that man-made invention by millions of years! Each sting is actually a hollow hair stiffened by silica with a swollen base that contains the venom. The tip of this hair is very brittle and when brushed against, no matter how lightly, it breaks off exposing a sharp point that penetrates the skin and delivers its stinging payload. It used to be thought that the main constituent of the sting was formic acid - the same chemical used by ants, giving that never forgotten burning sensation that demands to be scratched. Although formic acid is present in the sting, recent research has shown that the main chemicals are histamine, acetylcholine and 5-hydroxytryptamine (serotonin). A fourth ingredient has yet to be identified. Remember when stung a natural remedy will often be found close at hand. The leaves of the dock contain chemicals that neutralise the sting and also cool the skin.