Common foods involved include cow's milk, peanuts, eggs, shellfish, tree nuts, wheat, rice, and fruit.[1][2][3] Which allergies are most common depends on the country.[1] Risk factors include a family history of allergies, vitamin D deficiency, obesity, and high levels of cleanliness.[1][2] Allergies occur when immunoglobulin E (IgE), part of the body's immune system, binds to food molecules.[1] It is usually a protein in the food that is the problem.[2] This triggers the release of inflammatory chemicals such as histamine.[1] Diagnosis is usually based on a medical history, elimination diet, skin prick test, blood tests for food-specific IgE antibodies, or oral food challenge.[1][2]