A person with a food allergy can have symptoms beginning as soon as 2 minutes after eating the food, but reactions may take 1 to 2 hours to appear. Occasionally, symptoms abate quickly, only to recur in 3 to 4 hours.The most common symptoms include:Itching followed byHives,A rash of raised, andReddish bumps or whealsLip and mouth swellingBelly (stomach) crampsNauseaVomitingDiarrheaOther symptoms of food allergies may include:Itching and watering in the eyesRunny or stuffy noseSymptoms of a more severe reaction to foods or drinks could include:Shortness of breath or difficulty breathingTightness in the chestFeeling of tightness or choking in the throatRapid or irregular heart beatFeeling dizzy or light-headedLosing consciousnessA severe allergic reaction can be life threatening. This severe reaction is referred to as anaphylaxis, or anaphylactic shock. Signs and symptoms of anaphylactic shock are:Dizziness, lightheadedness, and loss of consciousness due to dangerously low blood pressure, called "shock."An anaphylactic reaction can begin suddenly, or it may develop gradually with itchiness and swelling of the skin and throat and then progress to a severe reaction over a few hours.Most people get such a reaction immediately after eating the food, but in a few unusual cases the reaction occurs only after exercising following the ingestion of the food.Severe reactions are most often seen with allergies to nuts, fish, and shellfish, although allergy to any food can cause anaphylaxis.People with asthma, childhood allergies, eczema, or prior severe food allergies are especially at risk for having an anaphylactic reaction.MSG reaction can be mistaken for an allergic reaction. Symptoms and signs of MSG reaction include:Burning sensation at the back of the neck and radiating down the arms and chestTingling and numbness in the same areasHeadacheNauseaOccasionally, difficulty breathing, especially in those with poorly-controlled asthmaA few people experience seizures, irregular heartbeats, and anaphylaxis after the use of MSG.Contrary to popular beliefs, MSG has no relation to Alzheimer disease, Huntington chorea, or other chronic illnesses.