If you have a peanut allergy, it means your body is overreacting to the proteins in peanuts. Instead of understanding that peanuts are safe (and tasty), your immune system thinks that peanuts are out to harm you. As a response, your body releases an antibody called immunoglobulin E whenever you ingest peanut proteins. In turn, the antibody triggers a bunch of chemicals to fight off the invading peanut allergen. The part of the fight between the allergen and your immune system that you feel are your allergic symptoms, which might range from hives to the potentially fatal anaphylaxis.
Doctors don't want you to take any chances with your peanut allergy. That means not only eliminating peanuts themselves, but also avoiding anything made with peanut byproducts -- peanut oil included. In fact, people with peanut allergies are recommended to stay away from foods made in a plant that process peanuts or in a kitchen that handles peanut products. The proteins from the peanuts or peanut oil might remain on the kitchen utensils and get onto your ostensibly peanut-free food, resulting in what is known as cross-contamination and an allergic response from your immune system.
The list of peanut allergy pitfalls doesn't stop at the word "peanut." Beware of the terms "hydrolyzed plant protein" and "hydrolyzed vegetable protein" in ingredient lists; both are code for "contains peanuts." Many ethnic dishes include peanuts and peanut oils, as do many baked goods. The key to avoiding setting off your peanut allergies is to always know what you're eating and where it came from. The other side of the peanut-allergy coin is to always be prepared, just in case you accidently ingest something with peanut proteins in it. Have your necessary treatment on hand -- whether it's an EpiPen or a pack of antihistamines.