An allergy to peanuts is your body's overreaction to certain proteins in peanuts. Your immune system misidentifies those proteins and thinks they're dangerous; in response, it sends out an antibody called immunoglobulin E to take care of the allergens. The antibody then triggers other chemicals to go out and fight the proteins. One of those chemicals, histamine, is responsible for many of the allergic symptoms you suffer.
If you're allergic to peanuts, symptoms normally kick in within a couple of minutes after you're exposed to the allergen. Symptoms can be mild or severe, depending on your allergic sensitivity. Skin-based symptoms of a peanut allergy include hives, redness, swelling and itching. Stomach problems that can result from a peanut allergy include cramps, nausea, diarrhea and vomiting. Peanut allergies can also cause respiratory symptoms, like sneezing, itchy eyes, runny nose, congestion and the trigger of asthmatic coughing and wheezing. The most dangerous of the symptoms of a peanut allergy is anaphylaxis, and peanut allergies are one of the leading causes of anaphylaxis. This condition is potentially life-threatening. The signs of anaphylaxis are constricted airways that make breathing difficult, a sudden and drastic drop in blood pressure, a fast pulse, dizziness and loss of consciousness. If you experience any of these symptoms at the same time, immediate medical attention is required. Many people with peanut allergies carry an injection of epinephrine with them in order to treat anaphylaxis before they reach the emergency room.
An allergic reaction to peanuts can be triggered by the direct consumption of peanuts, but it can also happen if food you're eating accidentally came in contact with peanuts. For some people, just inhaling dust, flour or steam with peanut traces is enough to set off an allergic reaction.