If you have a peanut allergy, you should avoid eating pesto. Pesto is a sauce made from crushed peanuts, basil, and olive oil. It is commonly used on pasta and other Italian dishes. Peanuts are one of the most common food allergens, and even a small amount can trigger an allergic reaction. Symptoms of a peanut allergy include itching, swelling, and difficulty breathing. If you have a severe allergy, you may experience anaphylaxis, which is a life-threatening reaction. If you are unsure whether a dish contains peanuts, it is best to avoid it.