In a nut allergy, the immune system overreacts when you eat nuts. Normally, the immune system helps keep you healthy by defending against harmful germs. But in a nut allergy, the immune system thinks something in the nuts is harmful. So it fights back with an allergic reaction. Sometimes this causes serious or dangerous symptoms.
The best way to treat a nut allergy is to avoid any food that might have nuts. And make sure that you know what to do if you accidentally eat something with nuts in it.