What are the symptoms of a food allergy?

A child’s reaction can also be different every time they’re exposed to the allergen, so it’s important to be aware of all the possible symptoms. A reaction may be more severe if a child eats more of the food they’re allergic to, if they’re sick or if they’ve exercised before or after being exposed. Five to 15 percent of anaphylactic episodes—in which two or more body systems are involved—are associated with exercise. On the other hand, having mild symptoms doesn’t predict that they’ll always be mild, says Kim. “It’s really difficult to predict who is going to have anaphylaxis later in life. The important thing is to be prepared.” Here’s what to look for:

The skin is one of the organs that is most often involved in food allergy reactions. One of the most common skin symptoms to occur after your child is exposed to an allergen is a rash or hives—an outbreak of swollen, pale red bumps or plaques (wheals) that can appear suddenly. You might also hear your kid complain about feeling itchy, which can occur on the skin or in their mouth (the tongue is a common spot for itching or discomfort), and their skin may look flushed or feel warm to the touch. You may also see swelling of the face, lips or tongue.

Respiratory tract symptoms triggered by a food allergy may include coughing, wheezing, shortness of breath (difficulty breathing), chest pain or tightness, throat tightness, hoarse voice, nasal congestion or hay fever-like symptoms (runny, itchy nose and watery eyes, sneezing), trouble swallowing. Respiratory symptoms may accompany skin and gastrointestinal symptoms, but don’t usually appear alone.

Gastrointestinal reactions to food allergies are also common. In the stomach and digestive tract, symptoms may include nausea, abdominal pain or cramping, vomiting or diarrhea. These symptoms may happen minutes after exposure to an allergen, but sometimes they can take place several hours after being exposed.

Food allergy reactions affecting the cardiovascular system (the heart) may include paler than normal skin colour, skin that appears blue, a weak pulse, passing out, dizziness, lightheadedness, fainting or shock. Some of these severe symptoms, alone or combined with other milder symptoms, may be signs of life-threatening anaphylaxis and require immediate treatment.

● Pale or blue skin ● Light-headedness ● Dizziness ● Grogginess ● Lethargy ● Weak pulse ● Fainting ● Shock

Neurological symptoms affecting the brain and mental health may also be triggered by food allergies and include anxiety. Your child may complain of a headache, a sense of doom (a feeling that something bad is about to happen) or a feeling that something is wrong with their body.

A severe allergic reaction is known as anaphylaxis and is a life-threatening medical emergency. Anaphylaxis comes on quickly and typically involves two or more body systems, such as the skin and cardiovascular system. On its own, a drop in blood pressure, which can show up in symptoms like dizziness and weakness, can also be a sign of anaphylaxis. If you suspect anaphylaxis, your child needs to be taken to the ER immediately.

“If a child gets really groggy really quickly after eating a food, that on its own might be a sign of a severe allergic reaction,” says Kim. “Some of the worst reactions we’ve seen are where blood pressure drops without anything else happening, and that can be life-threatening.”

The most serious signs of anaphylaxis are difficulty breathing and a drop in blood pressure, both of which can be fatal if left untreated. Anaphylactic shock occurs when low blood pressure affects the major organs, such as the brain and heart.

Children with asthma are more likely to experience anaphylaxis, and those who have a history of anaphylaxis are more likely to experience it again. A Canadian study published in 2017 found that children who have visited the emergency department for anaphylaxis have nearly an 18 percent chance of readmission every year.

Older children are also more likely to experience anaphylaxis. “Severe anaphylaxis in babies is fairly uncommon,” says Kim. “Babies become allergic over time, so it won’t happen immediately.”

It can be challenging for parents to recognize an allergic reaction in an infant or a toddler because they can’t verbalize their symptoms. “It’s not that uncommon that a baby has two or three reactions before the parents realize that it’s a real allergy,” says Kim.

Also, some symptoms may be missed because they resemble other issues. For example, parents may assume a drowsy baby simply needs a nap or that hives are from a viral infection (hives from a viral infection come and go over a period of days, while those from an allergic reaction set in soon after eating and go away within an hour).

A baby may grab at their mouth or throat or start fussing or crying, and an older child may say things like “My tongue is itchy” or “My throat is tight.”

What to do next

Read more: When your child’s food allergy leads to anxiety
How to know if your kid has a food allergy or food intolerance