It’s pretty common to have a reaction to a certain food, but in most cases it’s an intolerance rather than a true allergy. Why does it matter? Although they may have similar symptoms, a food allergy can be more serious. These clues can help you figure out if it is an allergy or intolerance. A doctor can help you know for sure. Food Allergy: Usually comes on suddenly

Small amount of food can trigger

Happens every time you eat the food

Can be life-threatening Food Intolerance: Usually comes on gradually

May only happen when you eat a lot of the food

May only happen if you eat the food often

Is not life-threatening

Different Symptoms When a food irritates your stomach or your body can't properly digest it, that’s an intolerance. You may have these symptoms: Gas, cramps, or bloating

Heartburn

Headaches

Irritability or nervousness A food allergy happens when your immune system mistakes something in food as harmful and attacks it. It can affect your whole body, not just your stomach. Symptoms may include: Rash, hives, or itchy skin

Shortness of breath

Chest pain

Sudden drop in blood pressure, trouble swallowing or breathing -- this is life-threatening. Call 911 immediately.

Common Food Allergies and Intolerances These triggers cause about 90% of food allergies: Peanuts

Tree nuts (such as walnuts, pecans and almonds)

Fish

Shellfish

Milk

Eggs

Soy

Wheat The most common food intolerance is lactose intolerance. It happens when people can’t digest lactose, a sugar found in milk and dairy. Another kind of intolerance is being sensitive to sulfites or other food additives. Sulfites can trigger asthma attacks in some people. What about a gluten allergy? While celiac disease -- a long-lasting digestive condition that’s triggered by eating gluten -- does involve the immune system, it doesn’t cause life-threatening symptoms.