Stinging Nettle - Nature's funny way of working. Most of us cross stinging nettle's path when out hiking and enjoying our time outdoors. Contact with bare skin results in small hairs from the leaves breaking off in your skin. These hairs inject formic acid and histamine. The chemical combination produces a rash and a burning or stinging sensation. If you happen to be allergic to it, stinging nettle can cause swelling. As uncomfortable or even as severe as the symptoms can be in some cases, …