Peanut allergy occurs when your immune system mistakenly identifies peanut proteins as something harmful. When you have direct or indirect contact with peanuts, your immune system releases symptom-causing chemicals into your bloodstream. It isn't known exactly why some people become allergic to peanuts and others don't.

Exposure to peanuts can occur in different ways:
- Direct contact. The most common cause of peanut allergy is eating peanuts or peanut-containing foods. Sometimes direct skin contact with peanuts can trigger an allergic reaction.

- Cross-contact. This is the unintended introduction of peanuts into a product. It's generally the result of a food being exposed to peanuts during processing or handling.

- Inhalation. An allergic reaction may occur if you inhale dust or aerosols containing peanuts, such as that of peanut flour or peanut oil cooking spray.

Food allergy vs. food intolerance
In some cases, what may appear to be a food allergy may actually be a food intolerance. Unlike a true food allergy, a food intolerance doesn't involve the immune system. With a true food allergy, even tiny amounts of the food can cause a severe reaction. In most cases, someone who has a food intolerance can eat small amounts of the food with only mild symptoms, such as indigestion or heartburn.