An adverse reaction to a food can come from either a food allergy, which is immune mediated, or food intolerance, which is a digestive system response. Many people think these two terms mean the same thing, but they don’t.

What is food intolerance?
Food intolerance is caused when a food irritates a person’s digestive system or when a person is unable to properly digest or break down the food. Intolerance to lactose, which is found in milk and other dairy products, is the most common food intolerance. Symptoms of food intolerance may include abdominal cramps, bloating and diarrhea.

What is a food allergy?
Food allergy occurs when the immune system reacts to a component of food, usually a protein or part of a protein known as a food allergen or antigen. Ingestion of the offending food causes the allergen to react with the allergic antibody (IgE) that then triggers the sudden release of histamine and other chemicals. This results in allergic reaction symptoms.

Symptoms of food allergy
These symptoms usually occur within minutes of food exposure:

• Tingling sensation in the mouth and throat
• Swelling of the tongue, lips and /or throat
• Flushing of the skin or rash
• Eczema or a worsening of eczema
• Hives and swelling
• Nausea and vomiting
• Abdominal cramps with diarrhea
• Wheezing and/or throat tightness
• Difficulty breathing
• Drop in blood pressure
• Loss of consciousness

Who is food allergenic?
Although food allergy symptoms are reported by 12 percent or more of people, studies have shown that the actual percentage of children proven to be food allergic is 3 to 4 percent. While younger people are more likely to be food allergic, older people are less so, at about 1 percent. Food allergies account for 30,000 visits to the emergency room each year.
Common food allergens
Ninety percent of food allergy reactions are caused by the following foods:

• Milk
• Eggs
• Fish (e.g., bass, flounder, cod)
• Crustacean shellfish (e.g. crab, lobster, shrimp)
• Tree nuts (e.g., almonds, walnuts, pecans)
• Peanuts
• Wheat
• Soybeans

Diagnosis of food allergies
To diagnose and treat a food allergy, the first thing your doctor will do is a complete medical and food history and physical prior to skin or blood testing. You will be asked about contents of the foods, severity and nature of your symptoms and the amount of time between eating and any reaction.

With allergy skin testing, a small amount of extract made from the food is placed on the back or arm. If a raised bump or small hive develops within 20 minutes, it indicates a possible allergy. If nothing develops, the test is negative. It is uncommon for someone with a negative skin test to have a true food allergy. Current methods of skin testing are very simple and can be performed on children and adults of all ages.

For patients with skin disorders or those taking certain medications, a skin test cannot be done, and a blood test may be recommended. If you have already had a food allergy blood test, be aware that not all blood tests are the same or considered accurate and reliable. False positive results may occur with both skin and blood testing and a food challenge(s) may be required to confirm the diagnosis. Food challenges are performed by consuming the food in our office, under supervision, to confirm a positive reaction.

Treatment
The best way to treat food allergy is to avoid the foods that trigger your allergy.

Always ask about ingredients when eating at restaurants or when eating foods prepared by anyone other than yourself.

We always encourage our food allergy patients to carefully read food labels. The United States and some other countries require that the eight major food allergens listed above are listed in common language.

Most importantly, we tell patients to always have and know how to use injectable epinephrine as well as an antihistamine to treat emergency reactions. Teach family members and others close to you how to use epinephrine. And wear an ID bracelet that describes your allergy.

If you have a known exposure to a food that has caused a prior reaction, it is often necessary to give yourself the epinephrine prior to symptoms developing. If a reaction occurs, have someone take you to the emergency room, even if symptoms subside. Afterward, get follow-up care from an allergist.

Co-authored by Drs. Richard Buck and Kraig Jacobson