Peanut allergy is a type of food allergy to peanuts. It is different from tree nut allergies, because peanuts are legumes and not true nuts. Physical symptoms of allergic reaction can include itchiness, hives, swelling, eczema, sneezing, asthma attack, abdominal pain, drop in blood pressure, diarrhea, and cardiac arrest. Anaphylaxis may occur. Those with a history of asthma are more likely to be severely affected.

It is due to a type I hypersensitivity reaction of the immune system in susceptible individuals. The allergy is recognized "as one of the most severe food allergies due to its prevalence, persistency, and potential severity of allergic reaction."

Prevention may be partly achieved through early introduction of peanuts to the diets of pregnant women and babies. It is recommended that babies at high risk be given peanut products in areas where medical care is available as early as 4 months of age. The principal treatment for anaphylaxis is the injection of epinephrine.

In the United States, peanut allergy is present in 0.6% of the population. Among children in the Western world, rates are between 1.5% and 3% and have increased over time. It is a common cause of food-related fatal and near-fatal allergic reactions.