• Question: Why do nettles sting? What causes this and how is it sore on the human skin?

    Asked by Lego Rules to Áine, Ciarán, Eoin, Lydia, Victoria on 20 Nov 2014.
    • Photo: Ciarán O'Brien

      Ciarán O'Brien answered on 20 Nov 2014:

      Nettle leaves are covered in tiny, brittle hairs called trichomes. These hairs are hollowed out and have chemicals in them. When a person brushes off them, they break open and act a little like syringe needles, injecting a little bit of the chemicals into the top layer of your skin. You probably don’t feel the injection at all, but the stuff it injects is a different kettle of fish…

      You might have heard of people with allergies taking antihistamines? They’re kind of like the opposite of histamine, because histamine CAUSES an allergic reaction, and there’s lots of it in a nettle sting.

      The sting isn’t caused by the histamine (although it does make the sting really itchy!), the nettle sting also contains a cocktail of other chemicals that cause the pain you get from a nettle sting. Some of the chemicals include moiridin (causes a painful burning sensation), Leukotriene (causes inflammation/swelling), formic acid (more burning sensation, it’s the same thing in an ant bite) and, bizarrely, acetylcholine and serotonin, which are neurotransmitters. Serotonin is usually one of the chemicals your brain releases when it’s happy, so I’ve no idea what it’s doing in a nettle sting. But acetylcholine is important to motor function so it might give the pain signals a bit of a boost to the brain to make it feel worse than it is.

      So that’s how nettles sting. Different species of nettle might have different combinations of the chemicals I mentioned but they all use the same method 🙂

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