Why are chestnuts poisonous?

Why Horse Chestnuts Are Toxic

If you have ever spotted shiny brown chestnuts littering the ground in autumn, you might be tempted to pick them up. However, unlike the sweet chestnuts you roast for the holidays, their lookalikes—commonly known as horse chestnuts—are completely inedible and harmful if consumed.

The main reason these nuts are dangerous is the presence of a natural chemical compound called aesculin (along with other toxic saponins). This toxin is found in every single part of the tree, including the leaves, bark, twigs, and the nuts themselves.

When ingested by humans or animals, aesculin disrupts normal bodily functions and can cause severe symptoms. These usually include painful digestive issues such as stomach cramps, nausea, vomiting, and diarrhea. Because the risk of poisoning is so high, it is best to admire horse chestnuts from a distance and leave them for the wildlife, which are naturally adapted or less susceptible to their effects.