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Image of the Week: Stinging Nettle

21 Aug, 2015

B0006134 Stinging hairs on a nettle leaf

It’s all part of the classic British summer – picnics, intermittent heat waves, sudden rain showers – and the burning sensation of an unexpected nettle sting.

Our image this week shows the surface of a stinging nettle (Urtica dioica) leaf, in far more detail that can be seen by the naked eye. Using a scanning electron microscope (SEM) an electron beam is passed over the surface of the sample, and incredibly detailed images are produced from the resulting signals.

What we can see in the image above is the surface of a stinging nettle leaf covered in fine hairs. The larger ones deliver the sting, and these stinging hairs are hollow tubes with walls made of silica, making them into tiny brittle glass needles. When you brush past them the tips of these hairs easily break, and their sharp tips pierce the skin, releasing the toxic liquid that causes us to yelp!

At the base of each hair sits a bulb containing the stinging concoction which includes formic acid (the same toxin as an ant bite), histamine (which causes inflammation in the body), acetylcholine and serotonin – the neurotransmitters that get our nervous system firing.

Once stung, you may feel the effects for up to 12 hours, though antihistamine or cortisone cream can help soothe the itching. You may choose to hunt for a dock leaf – long believed to help provide relief from nettle stings – but there is no evidence that these provide anything more than placebos. (The act of searching them out may take your mind off the pain at least!)

While many choose to avoid nettles due to their sting, cooking them destroys their venom and they are used to make nettle soup, nettle tea and even Cornish Yarg cheese!

Nettles have been used medicinally for hundreds of years to treat various ailments including painful muscles and aches, urinary tract infections, hayfever and benign prostatic hyperplasia. Evidence for effectiveness differs for these conditions, and it is important that you don’t self-medicate with nettle as it can interfere with other medications, such as blood thinners, drugs for blood pressure and diuretics.

Image credit: Liz Hirst, Wellcome Images CC-BY-NC-ND 4.0

Wellcome Images is one of the world’s richest and most unusual collections, with themes ranging from medical and social history to contemporary healthcare and biomedical science. Over 100,000 high resolution images from our historical collections are now free to use under the Creative Commons-Attribution only (CC-BY) licence

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