Why stinging nettles cause pain?

Stinging nettles are known for their annoying sting and the subsequent painful reaction they cause when they come into contact with the skin. These plants, often considered as weeds, have small hollow hairs on their leaves and stems that are responsible for the unpleasant sensation they induce. Let's take a look at the science behind why stinging nettles cause pain.


The anatomy of a stinging nettle hair

The stinging nettle hairs, also known as trichomes, contain a complex mixture of chemicals that cause the painful reaction. These hairs are hollow and easily break upon contact, allowing them to penetrate the skin. The main substances found in stinging nettle hairs are histamine, acetylcholine, and various irritants.


The body's response

When the hairs of a stinging nettle pierce the skin, the chemicals are released and come into contact with nerve endings. This triggers a cascade of reactions in the body. Histamine, a well-known substance released during allergic reactions, plays a significant role in causing itchiness, redness, and swelling. It activates receptors on the nerve endings, leading to itchy and painful sensations.

Acetylcholine is a neurotransmitter involved in the transmission of nerve signals. It stimulates pain receptors and contributes to the burning sensation experienced after contact with stinging nettles.

Additionally, stinging nettles contain irritants such as formic acid and serotonin. These substances contribute to the inflammatory response and enhance the experience of pain.


Evolutionary protection

While stinging nettles can be painful for humans, they have developed these defense mechanisms as a survival strategy. The presence of irritants and the painful reaction discourage animals and insects from eating them or walking through them. This has allowed stinging nettles to spread and survive.