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). Allergies to citrus fruits such as grapefruit are fairly common, though they are more common in adults than in children.

Some symptoms of a grapefruit 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.

Citrus allergy symptoms may occur from consuming a tiny amount of citrus fruit or fruit juice, or just from touching the peel or breathing in airborne particles of the fruit. Symptoms may appear immediately or several hours after coming into contact citrus fruit.

If you have any of the symptoms listed above after consuming or coming into contact with grapefruit you should see an allergist for a diagnosis and treatment. It is important to note that even if you do not have a grapefruit allergy, grapefruit can cause adverse reactions if you eat it or drink its juice it while taking certain medications. Some of the chemicals in grapefruit products can interfere with your ability to metabolize the medications, meaning that the medication will stay in your body for a longer period of time, building up to potentially dangerous levels. Always check with your doctor or pharmacist about interactions with grapefruit when you are prescribed a new medication.