Some people are allergic to sugar. This doesn't happen with sugars and fats. Milk allergy is very common and causes diarrhea in adults. It isn't a true allergy. People with food allergies are allergic to many foods.
Food allergy makes people hyperactive.
The most common chronic illnesses associated with food allergies are eczema and asthma. Allergy to food dye is common. They may occur in less than one of 100 children and in less than one of 500 adults. Food allergy is lifelong, or is always outgrown. However, allergies to peanuts, tree nuts, fish and shellfish are rarely outgrown.