The term allergy refers to the body’s immune system reaction to a foreign protein. Substances that trigger allergies can come from several sources. There are environmental allergens and foods allergens, as well as animal or plant allergens. Allergies tend to run in families. You are more likely to have a food allergy if other people in your family have allergies like hay fever, asthma, or eczema.
When you have a food allergy, your body believes certain foods are going to harm you. The body fights back by setting off an allergic reaction. In most cases, the symptoms of an allergic reaction are mild, but a serious reaction can be deadly.
Food allergies can be the result of food availability, culture, or unknown content of food products. Allergies to gluten, milk, eggs, soy and nightshade plants are a few of the most common. Food allergies are often undetected by standard allergy testing. Undiagnosed food allergies can result in symptoms of secondary conditions.

Some of the symptoms of food allergies include:

Digestive disorders
Eczema
Hives
Asthma
Runny nose
ADHD and ADD
Fibromyalgia
Muscle aches and joint aches
Chronic fatigue
Anaphylaxis (in serious cases)