About Milk Allergy

Almost all infants are fussy at times. But some are excessively fussy because they have an allergy to the protein in cow's milk, which is the basis for most commercial baby formulas.

A person of any age can have a milk allergy, but it's more common among infants (about 2% to 3% of babies), though most outgrow it.

If you think that your child has a milk allergy, talk with your doctor about testing and alternatives to milk-based formulas and dairy products.

A milk allergy occurs when the immune system mistakenly sees the milk protein as something the body should fight off. This starts an allergic reaction, which can cause an infant to be fussy and irritable, and cause an upset stomach and other symptoms. Most kids who are allergic to cow's milk also react to goat's milk and sheep's milk, and some of them are also allergic to the protein in soy milk.

Infants who are breastfed have a lower risk of developing a milk allergy than those who are formula fed. But researchers don't fully understand why some develop a milk allergy and others don't, though it's believed that in many cases, the allergy is genetic.

Typically, a milk allergy goes away on its own by the time a child is 3 to 5 years old, but some kids never outgrow it.

A milk allergy is not the same thing as lactose intolerance, the inability to digest the sugar lactose, which is rare in infants and more common among older kids and adults.

Symptoms of a Milk Allergy

Symptoms of cow's milk protein allergy will generally appear within the first few months of life, often within days or weeks after introduction of cow's milk-based formula into the diet. An infant can experience symptoms either very quickly after feeding (rapid onset) or not until 7 to 10 days after consuming the cow's milk protein (slower onset). Symptoms may also occur with exclusive breastfeeding if the mother ingests cow's milk.

The slower-onset reaction is more common. Symptoms may include loose stools (possibly containing blood), vomiting, gagging, refusing food, irritability or colic, and skin rashes, like eczema. This type of reaction is more difficult to diagnose because the same symptoms may occur with other health conditions. Most kids will outgrow this form of allergy after 2 years of age, although some might not outgrow it until adolescence.

Rapid-onset reactions come on suddenly with symptoms that can include irritability, vomiting, wheezing, swelling, hives, other itchy bumps on the skin, and bloody diarrhea.

In some cases, a potentially severe allergic reaction (anaphylaxis) can occur and affect the baby's skin, stomach, breathing, and blood pressure. Anaphylaxis is more common with other food allergies (peanuts and tree nuts) than with milk allergy.

Diagnosing a Milk Allergy

If you suspect that your infant is allergic to milk, call your doctor, who'll ask about any family history of allergies or food intolerance and then do a physical exam. There's no single lab test to accurately diagnose a milk allergy, so your doctor might order several tests to make the diagnosis and rule out any other health problems.

In addition to a stool test and a blood test, the doctor may order an allergy skin test, in which a small amount of the milk protein in inserted just under the surface of the child's skin with a needle. If a raised spot called a wheal emerges, the child may have a milk allergy. If your child is positive for a milk allergy, your doctor may tell you to avoid milk.

The doctor also might request an oral challenge test when he or she feels it is safe. This involves having the baby consume milk in the doctor's office, and then waiting for a few hours to watch for any allergic reaction. Sometimes doctors repeat this test to reconfirm the diagnosis.

Treating a Milk Allergy

If your infant has a milk allergy and you are breastfeeding, it's important to restrict the amount of dairy products that you ingest because the milk protein that's causing the allergic reaction can cross into your breast milk. You may want to talk to your doctor or a dietician about finding alternative sources of calcium and other vital nutrients to replace what you were getting from dairy products.

Since 2006, all food makers have been required to clearly state on package labels whether the foods contain milk or milk-based products, indicating this in or next to the ingredient list on the packaging.

If you're formula feeding, your doctor may advise you to switch to a soy protein-based formula. If your infant can't tolerate soy, the doctor may have you switch to a hypoallergenic formula, in which the proteins are broken down into particles so that the formula is less likely to trigger an allergic reaction.

Two major types of hypoallergenic formulas are available:

1. Extensively hydrolyzed formulas have cow's milk proteins that are broken down into small particles so they're less allergenic than the whole proteins in regular formulas. Most infants who have a milk allergy can tolerate these formulas, but in some cases, they still provoke allergic reactions.
   
2. Amino acid-based infant formulas, which contain protein in its simplest form (amino acids are the building blocks of proteins). This may be recommended if your baby's condition doesn't improve even after a switch to a hydrolyzed formula.

Unsafe Formulas

"Partially hydrolyzed" formulas also are on the market, but aren't considered truly hypoallergenic and can still provoke a significant allergic reaction.

The formulas available in the market today are approved by the U.S. Food and Drug Administration (FDA) and created through a very specialized process that cannot be duplicated at home. Goat's milk, rice milk, or almond milks are not safe and are not recommended for infants.

Switching Formulas

Once you switch your baby to another formula, the symptoms of the allergy should go away in 2 to 4 weeks. Your doctor will probably recommend that you continue with a hypoallergenic formula up until your baby's first birthday, then gradually introducing cow's milk into his or her diet.

If you have any questions or concerns, talk with your doctor.

Reviewed by: Archana Mehta, MD, and Sheelagh M. Stewart, RN, MPH
Date reviewed: October 2011