Food allergies occur when the body’s immune system sees a substance such as a particular food as a harmful “invader” and overreacts to it. The substances that cause allergic reactions are called allergens, which are what trigger an immune response, also called an allergic reaction.
8 Most Common Food Allergens
These major food allergens are responsible for 90% of food allergic reactions in the U.S.:
- Cow’s milk
- Eggs
- Fish
- Shellfish
- Tree nuts (e.g., almonds, walnuts, pecans)
- Peanuts
- Wheat
- Soybeans
Other common food allergens include:
What Are Symptoms of Food Allergies?
Symptoms of food allergies usually start within minutes of eating a particular trigger food but can occur up to about two hours after eating. Sometimes after the first symptoms go away, a second wave of symptoms returns one to four hours later (biphasic reaction).
Symptoms of food allergies may include:
- Stomach cramps
- Vomiting
- Hives or red, itchy skin
- Sneezing
- Itchy, watery eyes
- Stuffy or itchy nose
- Diarrhea
- Angioedema or swelling
- Anaphylaxis
- This is a severe allergic reaction that is a medical emergency
- Call 911 and get to a hospital’s emergency department (do not drive yourself) if you experience any of the following symptoms after eating:
- Chest tightness
- Difficulty breathing
- Tightness in the throat or a lump in the throat
- Hoarseness
- Wheezing
- Tingling in the hands, feet, lips, or scalp
How Are Food Allergies Diagnosed?
Allergies are diagnosed with a medical history and physical examination.
Tests used to diagnose food allergies may include:
- Skin prick food allergy test
- Blood tests (specific IgE, ImmunoCAP test)
- Physician-supervised oral food challenge tests
What Is the Treatment for Food Allergies?
- The main treatment for food allergies is to avoid the foods that trigger an allergic reaction.
- For mild allergic reactions, antihistamines may relieve symptoms.
- For people who have severe food allergies and may be prone to anaphylaxis, a doctor will likely prescribe auto-injectable epinephrine to carry at all times in the case of an anaphylactic reaction.
From 
https://www.allergyuk.org/information-and-advice/conditions-and-symptoms/36-types-of-food-allergy
https://www.aaaai.org/conditions-and-treatments/allergies/food-allergies
https://www.foodallergy.org/resources/common-questions
https://www.fda.gov/food/buy-store-serve-safe-food/food-allergies-what-you-need-know