While onions are not one of the more common food allergens, it is possible for both children and adults to suffer from an onion allergy. Symptoms of an onion allergy include flu-like symptoms, rash and inflammation. Depending on the severity of the allergy, sufferers can also develop a serious condition known as anaphylaxis. Allergy symptoms might appear almost immediately or occur several hours after consumption. Onion allergies can develop during childhood or later in life and might be accompanied by an allergy to garlic, chives and other members of the Allium family.
Many people who suffer from these allergies experience flu-like symptoms shortly after consuming onions. These symptoms frequently include upset stomach, diarrhea and nausea. Individuals who do not suffer from diarrhea might instead become constipated and bloated. Many people also experience headaches, sinus pain and trouble sleeping. Symptoms range from mild to severe and can last for several hours after consumption.
An allergy to onions might also produce several common symptoms of allergies, including hives, itching and inflammation. The lips, throat and face might become swollen, red and tender to the touch. It is also common for the eyes to become watery and irritated.
While rare, an onion allergy might lead to a condition known as anaphylaxis in some sufferers. Anaphylaxis is a serious medical condition that can cause changes in heart rate, difficulty breathing and unconsciousness. A person suffering from this condition might suddenly become lightheaded, confused or very swollen. People who believe they might be suffering from anaphylaxis should seek immediate medical attention as this condition can be fatal.
The symptoms of an onion allergy can develop anywhere from minutes to hours after consuming onions. Depending on the severity of the allergy, some individuals will experience symptoms after just cooking with onions or eating onion-flavored foods. Others can consume cooked onions without incident, but develop symptoms after eating raw or undercooked onions. It is also important to remember that individuals who are allergic to one type of onion might be sensitive to several types of onions. People who have allergies might also be allergic to other members of the Allium family, including chives, garlic and scallions.
While some people might begin showing signs of an onion allergy during childhood, others do not develop this allergy until adulthood. It is possible to suddenly develop an allergy after consuming a certain food for years. Since this can make it difficult to pinpoint the allergen, sufferers might need to contact a physician or specialist experienced in diagnosing food allergies to help determine the cause of their symptoms.