It's not called "stinging nettle" for nothing: if you're going to spend time in a nettle patch, cover up. The hairs on nettle's leaves and stems are miniature hypodermics, waiting to pucture your skin, which - ouch! - stings, then burns, then aches. But on arthritic joints, that sting stimulates, then exhausts, the production of pain messengers to the brain. Nettle leaf soup (cooking neutralizes the sting) has been found to reduce pain and immobility in people suffering from rheumatoid arthritis. Nettles have anti-inflammatory and diuretic properties, and although it's not clear why, chemicals in nettle roots help relieve symptoms of benign prostatic hyperplasia, or BPH.
(podcast: The Plant Detective, 7/26/14)