The most common allergic conditions include hay fever, asthma, skin, and food allergies. The basic cause of allergy is unknown.
Allergies run in families, but there are other factors as well.
For example, breast fed babies are less likely to have allergies than are bottle fed babies. It is not known why a person can become sensitive to some things and not to others. Many substances are capable of causing an allergic reaction. The most common are pollen, mold, house dust, animal hair and dander, feathers, food, drugs, and insect stings. These allergens cause different kinds of allergic reactions.