Thanks for your responses. She was given formula in the hospital at birth and also supplemented for a few weeks at home but was breastfeed for 2 years. She's only had one vaccine hepB in the hospital. I don't recall ever eating peanut butter or peanuts while pregnant or nursing (maybe once but I don't recall). Noone else in her family that we know of is allergic to peanuts. We usually eat organic food and are anti-junk food. It is kind of a mystery to me. She used to be allergic to dairy and strawberries when very young but she has outgrown all other allergies.