Stinging hair of nettle leaves inject fluid in the human body causing burning pain. The fluid is

Nettle (Urtica dioica) is a herbaceous plant found in the wild that possesses stinging hairs on its leaves and stems [2]. These hairs function like hypodermic syringes; when touched, the bulbous tip breaks off, injecting a cocktail of chemicals into the skin [4]. According to standard educational texts, the primary fluid injected that causes burning pain and irritation is methanoic acid, also known as formic acid [3]. While modern scientific research indicates that the sting's chemistry is complex—containing neurotransmitters like histamine, acetylcholine, and serotonin, as well as traces of tartaric and oxalic acids—methanoic acid remains the classically identified irritant in this context [2]. The acidic nature of the sting is traditionally neutralized by applying a base, such as baking soda or the alkaline sap of a dock plant [3].

Sources

1. [2] https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/stinging-hairs
2. [3] https://www.science.gov/topicpages/n/nettle+urtica+dioica
3. [4] https://pmc.ncbi.nlm.nih.gov/articles/PMC7918447/
4. [1] Science , class X (NCERT 2025 ed.) > Chapter 2: Acids, Bases and Salts > Nature provides neutralisation options > p. 28