Symptoms of Allergic Reactions

For information on how to safely introduce allergens, see our Introducing Allergens guide, the First 100 Days Meal Plan or watch our course videos on how to introduce common food allergens.

Is my baby having an allergic reaction?

Allergic reactions to food typically occur within two hours of consuming the allergenic food—and often just minutes.1 There is, however, a small percentage of babies who may experience a delayed allergic reactions, typically due to FPIES.

Generally, the more of the allergen consumed, the more severe the reaction is likely to be, so it is important to start small when introducing new foods to your baby. Lastly, your baby may not have an allergic reaction the first time they are exposed to the food, so be watchful on the second and subsequent exposures. 

If you think your baby is having an allergic reaction, call emergency services immediately.

Symptoms of an allergic reaction vary from baby to baby, and can range from mild to severe. Generally, the severity of a reaction is judged by how many symptoms are present and the severity of those symptoms. Before you introduce potential allergens into your baby’s diet, know how to recognize the signs of an allergic reaction.

Common symptoms of an allergic reaction are described below.2

Symptoms of mild allergic reactions:

Mild symptoms of an allergic reaction can include ONE of the following (more than one would constitute a more severe reaction):

  • Itchy or runny nose, sneezing
  • Itchy mouth
  • A few isolated hives, mild itching
  • Mild nausea or gastrointestinal discomfort

If you note any of the above symptoms, stop feeding the allergen and contact your pediatrician, family practitioner, or allergist for guidance. If your child is having multiple symptoms, call 9-1-1/local emergency services immediately and request an ambulance with autoinjectable epinephrine.

Mild allergic reaction with isolated blotches around the mouth. Note: acidic foods such as tomato, lemon, and strawberries can cause a harmless but similar looking skin irritation around the mouth.
A mild allergic reaction with isolated hives on the back of the leg.

Symptoms of severe allergic reactions in babies:

More severe reactions may include any of the following, either alone or in combination:

  • Shortness of breath, wheezing, repetitive cough
  • Pale, ashen or bluish skin
  • Swelling of face, lips, or tongue
  • Widespread hives on body
  • Repetitive vomiting
  • Sudden tiredness/lethargy/seeming limp

If your child is having any of the above symptoms, call 9-1-1/local emergency services immediately and request an ambulance with autoinjectable epinephrine. Do not wait.

A severe allergic reaction with widespread hives and rash.
A severe allergic reaction with facial swelling.
Severe allergic reaction with eye and lip swelling.

a 9 month old with widespread rash in an allergic reaction
Severe allergic reaction with widespread rash and skin color changes.
a 10 month old with facial swelling and rash from allergic reaction to cashews
A severe allergic reaction with facial swelling and widespread rash and hives.
A severe reaction with widespread hives.
A severe reaction with widespread rash.
A severe reaction with facial rash and swelling.
A severe reaction with facial rash and swelling.
A severe reaction with facial rash and swelling.

Delayed symptoms & FPIES

FPIES (Food Protein-Induced Enterocolitis Syndrome) is a type of food allergy in children that can be severe and life-threatening. Unlike most allergic reactions (which can occur within minutes), FPIES allergic reactions occur within hours after consuming a particular food. For this reason, FPIES is sometimes known as a delayed food allergy. The most common food culprits of FPIES are cow’s milk products (such as formula), soy, oats, and rice, followed by other foods such as avocado, banana, barley, eggs, green beans, peas, meats, poultry, seafood, squash, and sweet potatoes. FPIES is extremely rare in exclusively-breastfed infants.3

The classic presentation of FPIES is an infant who recently switched from breast milk to formula or started solids and begins vomiting between 1 to 4 hours and experiencing diarrhea between 5 to 10 hours after eating the specific food culprit. Other symptoms include low blood pressure, low body temperature, extreme pallor, repetitive vomiting, and significant dehydration. Thankfully, most cases of FPIES will completely resolve during toddlerhood. If a child has been diagnosed with FPIES, they must be followed closely by an allergist or immunologist.

A 6-month-old baby vomits in his sleep during an FPIES reaction.

How do I tell the difference between an eczema flare-up and an allergic reaction?

While babies with severe eczema are at an increased risk of developing food allergy, it is important to note that most babies with eczema do NOT have a food allergy. In fact, only one third of moderate-severe eczema cases in babies can be directly associated with food allergens. Ingestion of a food allergen can result not only in immediate skin symptoms (redness, hives, itching, swelling), but can also result in a delayed flare-up of pre-existing eczema. Therefore, it can be difficult to know if baby’s eczema is occurring on its own, or if it was triggered by a previously unrecognized food allergen. For the most part, IgE-mediated allergic reactions to foods will appear quickly (within a few minutes to 2 hours after ingestion).

If there are no immediate signs of allergy (skin symptoms, respiratory distress, vomiting/diarrhea, etc.), and the only noted symptom is a delayed eczema flare-up that can be controlled with emollients and/or topical anti-inflammatory medication, the general recommendation is that the diet NOT be restricted. Eliminating a food from baby’s diet in the hopes of clearing up mild or moderate eczema may actually be counter-productive, potentially increasing the risk of baby developing a more serious allergy to that food in the future.

How do I tell the difference between rashes from acidic foods and an allergic reaction?

Rashes and skin irritation from eating acidic foods such as lemon, tomato, pineapple, orange and other citrus fruits are typically limited to the area where the food touched the skin and are short-lived; with some gentle washing, the rash should dissipate within ten minutes or so. With these kind of “contact rashes” (aka contact dermatitis) from the acidic foods, there are no other reactions or symptoms and the rash area is relatively small. For example, if baby has a widespread rash, such as all over their torso, it is likely an allergic reaction and not a contact rash. Similarly, if a baby has a short-lived rash on the chin (but no other symptoms), it is likely just a contact rash from the food or even baby’s own saliva.

Rashes that occur after contact with or ingestion of a food allergen are typically present with other symptoms, such as hives and itching. In these cases, allergy-inducing antibodies recognize proteins in the food allergen and trigger white blood cells in the skin (called mast cells) to release histamine and other chemical mediators of allergic reactions into the surrounding tissues. This causes redness, hives, and itching. This type of rash may or may not go away on its own, and may require medication or medical attention, depending on its severity.  As IgE antibodies and mast cells exist throughout the body, there is also a chance that the reaction might become more serious. Therefore, it’s important to seek medical guidance if the rash does not resolve quickly after washing.

Adie, 19 months, with a contact rash around her mouth from eating tomato.

Critical information for caregivers

Should you or your baby’s caregiver ever need to call 9-1-1/your local emergency services, things will move more quickly if you have the information below ready at-hand (this info is good to put in your own phone and on your refrigerator/wall for caregivers):

  • Birth date
  • Weight
  • Address
  • Insurance card (photo of, copy of)
  • Nearest hospital (or preferred hospital)
  • Special health info (e.g., baby was born prematurely at 30 weeks, etc.)

Reviewed by:

Dr. S. Bajowala, MD, FAAAAI. Board-Certified Allergist & Immunologist

For information on how to safely introduce allergens, see our guide on Introducing Allergens to babies, our course videos, or our First 100 Days guide on how to introduce common food allergens.

  1. FARE, Common Questions. [website]. (Retrieved March 3, 2020
  2. FARE, Treating Severe Allergic Reactions. [website]. (retrieved March 3, 2020)
  3. Nowak-Węgrzyn, A., Chehade, M., Groetch, M. E., Spergel, J. M., Wood, R. A., Allen, K., Atkins, D., Bahna, S., Barad, A. V., Berin, C., Brown Whitehorn, T., Burks, A. W., Caubet, J.-C., Cianferoni, A., Conte, M., Davis, C., Fiocchi, A., Grimshaw, K., Gupta, R., … Greenhawt, M. (2017). International consensus guidelines for the diagnosis and management of food protein–induced enterocolitis syndrome: Executive summary—Workgroup Report of the Adverse Reactions to Foods Committee, American Academy of Allergy, Asthma & Immunology. Journal of Allergy and Clinical Immunology, 139(4), 1111-1126.e4.