Onion and garlic allergies are caused by a hypersensitivity to these substances. When the immune system identifies onion and garlic as dangerous substances, immunoglobulin E antibodies are released into your blood stream. These antibodies fight against the onion and garlic proteins, causing mast cells in soft tissues throughout your body to produce histamine. Increased amount of histamine causes inflammation in tissues, which leads to common allergy symptoms.
Most food-related allergy symptoms cause inflammation in your lungs, sinuses, skin and digestive system. Symptoms typically develop within minutes of eating onion or garlic but can take up to an hour before surfacing. Common symptoms include chest tightness, shortness of breath, coughing, wheezing, sinus congestion, rashes, hives, facial swelling, abdominal pain, diarrhea, nausea and vomiting. If you develop severe symptoms, such as an increased heart rate, a metallic taste in your mouth, swelling in your lips, hives, lightheadedness and a sudden drop in blood pressure,then go to the emergency.These are signs of a severe allergic reaction that could lead to death.
If you accidentally ingest onion or garlic, you can take an antihistamine to treat mild to moderate allergy symptoms. Skin reactions can be treated with hydrocortisone to reduce the itch and inflammation in the skin. If you develop a severe allergic reaction, you may need an injection of epinephrine to restore your body.