What Causes Formula Allergy In Babies And How To Treat It?

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Formula allergy in babies is an immunological condition where the baby develops an allergy to formula or formula milk. Formula or formula milk is a substitute for human milk that contains the nutrients that support the growth and development of an infant (1). The formula is designed for babies whose mothers can’t breastfeed or have a low milk supply, which isn’t enough to meet their dietary needs.

While most babies consume formula without much concern, some may develop allergies. The allergy can be triggered by any of the ingredients in the formula, which may cause mild to severe allergy symptoms, depending on the severity of the allergic reaction. Prompt pediatric evaluation can help resolve the symptoms and avert complications.

Keep reading to know the causes, symptoms, and treatment for formula allergy in babies.

Is Formula Milk Allergy Common In Babies?

Most baby formulae use animal milk (cow) or plant milk (soy) as the protein source. According to the American Academy of Pediatrics (AAP), 80 percent of the commercial formulae are cow milk-based (2). Cow milk is a common food allergen, with cow milk protein allergy affecting about two to three percent of infants (3) (4).

According to the British Journal of General Practice, “The incidence of cow’s milk protein allergy (CMPA) in formula-fed babies is around five to seven percent (5)Besides, about 10 to 14 percent of babies allergic to cow milk exhibit reactivity to soy protein (6). Soy itself is a common allergen that can trigger an allergic reaction in babies.

What Is The Difference Between Formula Intolerance And Formula Allergy?

Formula intolerance and formula allergy are different conditions.

Formula intolerance is a non-immunological condition involving the digestive system. It is when the digestive system cannot break down certain formula milk compounds due to some underlying reason, leading to gastrointestinal discomfort. Food intolerances could develop due to congenital or acquired enzyme deficiencies, sensitivity to food additives, reactions to naturally occurring chemicals in foods, or accidental ingestion of a toxin/pharmacologic agent (7) (8).

Formula allergy is an immunological condition where the immune system mistakenly identifies milk proteins as pathogens and attacks them with antibodies. The immune response leads to an allergic reaction, causing symptoms such as hives (skin bumps) and tissue swelling. Allergies are usually more severe and life-threatening than food intolerances.

What Causes Formula Allergy In Infants?

The hypersensitivity and inappropriate action of the immune system towards formula lead to formula allergy. The immune system identifies one or more proteins in the formula milk as foreign entities or pathogens and attacks them. It ultimately triggers allergic reactions, the severity of which varies from one baby to another (9).

Heredity and environmental factors may play a role in the manifestation of baby formula allergy. For instance, the chances of a food allergy rise to about 75 percent if both parents have allergies (10). The baby may also have cross-reactivity where they could display hypersensitivity to other similar substances. For instance, a baby allergic to cow milk formula may also be allergic to goat milk formula.

Signs And Symptoms Of Formula Allergy In Babies

Formula allergy can be IgE or non-IgE mediated, wherein the signs and symptoms could appear immediately or hours and even days after ingesting the formula. Here are some signs and symptoms you should keep a check on (4) (6).

  • Itchy red bumps or skin rashes (hives)
  • Acute wheezing, blocked or runny nose
  • Acute vomiting
  • Swelling of the mouth, cheeks, lips, tongue, and throat
  • Abdominal cramps, diarrhea (possibly bloody), or constipation
  • Loss of appetite
  • Slow weight gain
  • Extreme irritability or colic

In some cases, formula allergy can cause a potentially severe allergic reaction (anaphylaxis), making the prompt diagnosis of the condition imperative.

Diagnosis Of Formula Allergy

There is no specific test to detect formula allergy. If you suspect your baby has formula allergy, consult a pediatrician promptly.

  1. Physical examination: During the physical examination, the doctor will collect the baby’s medical history, family medical history, and details about symptoms. The doctor may suggest an elimination test based on the information collected.
  1. Elimination diet test: In this test, your doctor will ask you to eliminate the current formula milk from your infant’s diet and reintroduce it after a week. If reintroduction causes a reaction, it indicates formula allergy. Your pediatrician may recommend additional tests to confirm it.
  1. Blood test: A blood test for formula allergy will estimate the number of antibodies present in the body. These antibodies are responsible for triggering an allergic reaction. Additionally, the doctor may ask for a stool test to help determine inflammation in the body, generally seen in milk allergy (11).
  1. Skin prick test: This test involves placing drops of formula milk on the back of the infant’s hand or forearm. The skin is then pricked using a sterile probe to let the milk enter the skin. If an itchy, reddish bump develops within 15 to 20 minutes, it indicates an allergy. This test is rarely conducted in babies younger than six months (12).

Based on the diagnosis, your doctor will suggest switching to a different baby formula and observing how the baby reacts. The next section contains some baby formulas that could be advised to a baby with formula allergy.

Can Formula Allergy Be Treated?

There is no cure or treatment for formula allergy. An infant with formula allergy is advised to use hypoallergenic formula. Below are some commercial formulae that your doctor could recommend, depending on your infant’s symptoms and tolerance  (5) (13).

1. Soy infant formula

Soy infant formula is made of soy protein isolate and is free from cow milk protein and lactose (14). Its use is often advised to babies with lactose intolerance. Some babies with cow milk allergy may develop soy protein allergy. However, term infants with IgE-mediated allergic reaction to cow milk protein may use soy-based formula (15).

2. Hydrolyzed protein formula

These are hypoallergenic formulas available in two types —partially hydrolyzed and extensively hydrolyzed.

  • Partially hydrolyzed protein formula contains cow milk protein (whey and casein) broken down into smaller proteins that are easy to digest. However, the hydrolysis is not enough to render the protein inactive to trigger an allergic reaction. Thus, this formula is not suitable for babies with cow’s milk allergy but may be beneficial to babies with a soy allergy.
  • Extensively hydrolyzed protein formula contains casein that is broken down into smaller, easy-to-digest form. About 90% of babies with cow’s milk allergy can tolerate this formula as it is easy to digest and does not trigger an allergy. Casein is the most common cause of cow milk allergy in babies.

3. Amino acid-based formula

Amino acid-based formula or elemental formula contains amino acids, which are the basic building blocks of proteins. This formula is well-tolerated by most babies. It is typically recommended for babies who are unable to tolerate even extensively hydrolyzed formula.

The USDA advises parents and caregivers not to change a baby’s formula without consulting a pediatrician. Speak to a pediatrician if you wish to try another type of formula for your baby with formula allergy.

Frequently Asked Questions

1. Does green poop mean milk allergy?

Green poop is associated more with milk intolerance or lactose intolerance than milk allergy (16). However, green stools alone cannot confirm if a baby is lactose intolerant. Hence, do not stop breastfeeding them until you consult a doctor.

2. Are formula-fed babies more likely to have allergies?

No, formula feeding has not been shown to increase babies’ risk of food allergy. However, introducing multiple sources of foods in the first three months may increase their risk of developing allergies (17).

Formula allergy in babies could result from an allergic reaction in response to any formula components. For example, it is common in babies fed formula made with cow milk and soy protein. Nonetheless, you must get your baby evaluated by a pediatrician if you notice any signs of allergy, such as excessive crankiness, vomiting after a feed, digestive issues, hives, appetite, or weight loss. The doctor may also suggest the right formula alternatives. Altogether, timely medical evaluation and management could help relieve your baby’s discomfort early.

Key Pointers

  • Most baby formulas are made from cow milk protein or soy protein, and they are both common allergens for babies.
  • Formula allergy is when the body’s immune system identifies the formula as a pathogen.
  • Formula intolerance occurs when the digestive system cannot process the formula and causes gastrointestinal issues.
  • Hives, wheezing, vomiting, and slow weight gain are some common signs and symptoms of a formula allergy.


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Swati Patwal

Swati Patwal is a clinical nutritionist, a Certified Diabetes Educator (CDE) and a toddler mom with over eight years of experience in diverse fields of nutrition. She started her career as a CSR project coordinator for a healthy eating and active lifestyle project catering to school children. Then she worked as a nutrition faculty and clinical nutrition coach in different... more

Dr. Dur Afshar Agha

Dr. Dur Afshar Agha is a consultant pediatrician with decades of experience in various medical facilities both in Pakistan and Saudi Arabia. She has headed the Department of Preventive Pediatrics at the prestigious, Children’s Hospital and Institute of Child Health in Pakistan and is a life member of the Pakistan Paediatric Association. She has also completed her Post Graduate Program... more