Your baby has a rash, is fussy after feedings, or has recurring stomach pain. You are wondering if it could be a food allergy.

It is a common and reasonable question. About 5–8 percent of children under school age have an allergy to one or more foods, according to the AAP and FARE (Food Allergy Research and Education). Recognizing the signs early makes it easier to act quickly and correctly.

This article gives you an overview of symptoms, what you should do, and when it is urgent.

What Is a Food Allergy?

A food allergy means the immune system reacts to proteins in food as if they are dangerous invaders. The body launches an inflammatory response, and that is what you see as symptoms.

An allergy is not the same as an intolerance. Lactose intolerance, for example, is caused by the body lacking an enzyme, not an immune reaction. The symptoms can look similar, but the cause is different.

Allergy vs. intolerance Food allergies involve the immune system and can cause serious reactions, even from very small amounts. Food intolerance (like lactose intolerance) is dose-dependent and rarely dangerous. Contact your pediatrician to find out which one your child has.

The Most Common Allergens in Babies

According to FARE and the AAP, these foods are responsible for the vast majority of allergic reactions in young children:

Cow's milk — the most common food allergy in infants, affects 2–3 percent
Eggs — one of the most frequent allergens in children under 2 years
Peanuts — can cause serious reactions, even from small amounts
Tree nuts — hazelnuts, cashews, walnuts
Wheat and gluten — often the first signs are digestive issues
Fish — common in many diets, but can trigger reactions
Shellfish — shrimp, crab, and similar
Soy — hidden in many processed products
Sesame — now officially a major allergen in the US (since 2023)

The good news: most children outgrow their allergy to milk, eggs, wheat, and soy during childhood.

Two Types of Reactions: IgE and Non-IgE

It is important to know that food allergies fall into two main types. They cause different symptoms and occur at different times.

Immediate Reactions (IgE-mediated)

Symptoms come quickly, often within minutes and at most two hours after the baby has eaten the allergen.

Typical signs:

Hives (raised, red patches on the skin)
Swelling around the mouth, on the lips, or in the face
Itching in the mouth or on the skin
Vomiting
Runny nose and eyes
In serious cases: difficulty breathing and anaphylaxis

Delayed Reactions (Non-IgE-mediated)

These reactions take longer, often 2–48 hours. They are harder to connect to a specific food, and they occur most often in infants.

Typical signs:

Blood or mucus in the stool (in an otherwise healthy baby)
Persistent diarrhea or constipation
Colic-like abdominal pain
Eczema that does not resolve
Poor weight gain
Excessive crying and fussiness after feedings

FPIES and FPIAP Two specific variants of non-IgE-mediated allergy are often seen in infants. FPIES (Food Protein-Induced Enterocolitis Syndrome) causes severe vomiting and diarrhea 2–4 hours after ingestion, and can lead to dehydration. FPIAP (Food Protein-Induced Allergic Proctocolitis) causes blood in the stool in an otherwise healthy baby. Both require evaluation by a doctor.

Cow's Milk Protein Allergy: The Most Common of All

Cow's milk protein allergy is the most frequent food allergy in the first year of life. It affects around 2–3 percent of infants, according to the AAP and FARE.

Symptoms can appear either through breast milk (if the mother drinks cow's milk) or directly from cow's milk-based formula.

Typical signs of cow's milk protein allergy in infants:

Rash and eczema, especially on the cheeks
Frequent vomiting
Loose stools or diarrhea
Abdominal pain and colic-like fussiness
Blood in the stool (in the FPIAP variant)
Poor weight gain over time

Are you breastfeeding? If your pediatrician suspects your baby is reacting to cow's milk protein through breast milk, you can try eliminating all dairy products from your own diet for 2–4 weeks. Do this under the guidance of a doctor or registered dietitian.

Parent caring for a child in a warm home setting

Symptoms by Body Part

It can help to think systematically. Allergic reactions are often grouped by which part of the body is affected.

Skin

Hives (urticaria): raised, red, and itchy patches
Eczema that flares up or does not resolve
Redness and swelling around the mouth after feeding
Itching without visible rash

Stomach and Gut

Vomiting shortly after feeding
Diarrhea or loose stools
Constipation that does not respond to treatment
Blood or mucus in the stool
Gas pain and fussiness

Airways and Mouth

Runny nose
Hoarseness or throat-clearing after feeding
Wheezing
Swelling of the lips or tongue

Anaphylaxis: The Most Serious Reaction

Anaphylaxis is an acute and life-threatening allergic reaction. It is fortunately rare in infants, but you should know the signs.

Call 911 immediately if your baby shows one or more of these signs:

Difficulty breathing, wheezing, or labored breathing
Swelling of the tongue, throat, or airway
Pale or bluish skin color
Limpness, loss of consciousness, or unusually low responsiveness
Persistent vomiting combined with other symptoms

Lay the baby flat with legs elevated while waiting for the ambulance. If your doctor has already prescribed an epinephrine auto-injector (EpiPen), use it immediately according to the instructions.

Anaphylaxis always requires follow-up with an allergy specialist afterward.

What to Do If You Suspect a Food Allergy

A series of unclear symptoms can be confusing. Here is a practical approach.

Step 1: Write Down What You See

Before you call your pediatrician, note what the baby has eaten, when the symptoms appeared, and what they look like. The more specific you are, the easier it is for the doctor to assess.

Step 2: Contact Your Pediatrician

Your pediatrician is the first stop. They will take a thorough history and assess whether further evaluation is needed. Avoid removing foods from the diet without medical advice, as this can make diagnosis more difficult.

Step 3: Testing — How It Works

Your pediatrician may refer you to a pediatric allergist for further testing. Possible investigations include:

Skin prick test (IgE-mediated allergy): The test is performed on the skin and shows whether the child is sensitized to specific proteins
Blood test (specific IgE): Measures allergy antibodies in the blood
Elimination and challenge diet: The most reliable method. The food is removed for a period, then reintroduced in a controlled way. Always done under medical supervision
Open or blinded food challenge: Used at specialist centers to confirm the diagnosis

Do not guess on your own An elimination diet without medical supervision can cause the child to miss important nutrients, and you may unnecessarily remove foods the child tolerates well. Always contact your pediatrician or a registered dietitian.

Step 4: Diet During Treatment

If an allergy is confirmed, the doctor and a registered dietitian will help create a safe meal plan. For cow's milk protein allergy, extensively hydrolyzed formula and elemental formula are available to fully meet the baby's nutritional needs.

Will My Baby Outgrow It?

Yes, for most children. Cow's milk protein allergy is among those most likely to resolve. Most children tolerate cow's milk by age 3, and nearly all are allergy-free by school age.

Peanut and tree nut allergies, however, tend to be more persistent, and few children outgrow them. It is important to follow up with an allergy specialist over time.

Caring parent with child in a calm atmosphere

Prevention: Early Introduction Protects

Recent research shows that early introduction of allergens can actually prevent allergies from developing. The AAP recommends that all infants be introduced to allergenic foods during the first year of life — including for babies at higher risk.

Read more about safe introduction in our guide: Allergens for babies: Safe introduction of allergenic foods

Want to track what your baby has tried? Use SmartStart food introduction for easy monitoring.

Frequently Asked Questions

Can my baby have a food allergy even if no one in the family is allergic?

Yes, it is possible. Family history of allergy increases the risk, but food allergy can develop without any known hereditary background.

Can my baby get a food allergy through breast milk?

Yes. Proteins from cow's milk, eggs, and other foods can be transferred into breast milk. If your baby is reacting while you are exclusively breastfeeding, your pediatrician may recommend trying to eliminate the relevant foods from your diet for a short period.

What is the difference between an allergy and lactose intolerance?

Lactose intolerance is caused by a deficiency of the enzyme lactase and causes stomach pain and diarrhea, particularly with larger amounts of milk. It is not an immune reaction. Food allergies involve the immune system and can cause serious reactions even from very small amounts.

How long does an elimination diet last?

It varies. The doctor determines the duration based on the child's age and symptoms, but 2–6 weeks is typical. After that, the food is tested again in a controlled way (food challenge).

Can my baby start daycare with a food allergy?

Yes. You have the right to inform the daycare about your child's allergy, and the facility is obligated to accommodate them. It is a good idea to have written documentation from a doctor, and to go through the meal plan with the staff.

What do I do if my baby has accidentally eaten an allergen?

Observe the child closely. Mild symptoms (slight rash, itching) can be monitored at home, but contact your doctor or urgent care. Serious symptoms (difficulty breathing, swelling of the throat, loss of consciousness) require calling 911 immediately.

Food Allergy in Babies: Signs, Symptoms, and What to Do