There are many different reactions your body could have from an allergen. The most serious (and sometimes life-threatening) reaction is anaphylaxis. It causes your immune system to release a bunch of chemicals that makes you go into shock. If someone you know goes into anaphylaxis shock, they’ll need an injection of epinephrine and to be taken to the emergency room right away. Anaphylaxis is rare, but can be fatal if not treated properly. Most allergic reactions aren’t quite as severe. Here’s a look at the most common signs and symptoms of allergies: