system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do onions irritate your eyes?
gpt
Its a defense mechanism. When its cells are destroyed it releases enzymes that break down amino acids. Its a chain reaction that creates organic compounds that contain sulfur, which smells bad and stimulates nerves in your eyes which causes them to sting.

This stops most animals from trying to eat them. The onion may be destroyed but the plant is left relatively unharmed. Soon, animals stop trying. Humans are not deterred by such defenses though, and cooking them stops this chain reaction completely.