Food allergies occur when the immune system identifies the proteins in a particular food as harmful to the body, subsequently reacting to try to "fight off" the "harmful" proteins (which are in fact harmless). Cow's milk is one of the "big eight" allergens that cause 90 percent of all food allergies. Yogurt is a common allergenic food when it is made from cow's milk, even though the production of yogurt requires processing and fermentation of the milk.

Some symptoms of a yogurt allergy include:

  • Itching or swelling of the mouth, tongue or lips
  • Skin reactions (eczema, hives, swelling and redness of the extremities or face)
  • Gastrointestinal symptoms (abdominal pain, nausea, vomiting, diarrhea)
  • Respiratory symptoms (runny or stuffy nose, coughing, sneezing, wheezing, difficulty breathing)
  • Cardiovascular symptoms (Drop in blood pressure, lightheadedness, fainting)

If you experience symptoms of anaphylaxis, which include nausea, vomiting, weak or rapid pulse, difficulty breathing, confusion and loss of consciousness, seek immediate medical attention, as this can be fatal. If you have common symptoms of a yogurt allergy you should see an allergist for proper diagnosis. Some allergy symptoms are similar to symptoms of a food intolerance. You may actually be lactose intolerant, meaning you are missing the intestinal enzyme that breaks down lactose (milk sugar). Treatment and management of dairy allergy and lactose intolerance are different, so it's important to know which one you have.

Some people who are allergic to milk are able to eat yogurt because the culturing process it goes through makes yogurt easier to digest than milk. In addition, just because you are allergic to yogurt made from cow's milk does not mean you are allergic to all yogurt. It's possible that you will be able to eat yogurt made from goat's milk or other types of milk.