If your baby frequently vomits or has diarrhea after drinking formula, they may be allergic to the cow's milk protein found in most formulas.
Formula allergies are typically caused by a cow's milk allergy. A cow's milk allergy is an atypical immune response in which the body reacts to the protein in milk as though it's a foreign invader that needs to be fought off.
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Cow's milk allergy is the most common food allergy in children. In fact, 2 to 3% of kids under age 3 show symptoms of this allergy.
"Cow's milk allergy is not to be confused with lactose intolerance," says Liz Donner, M.D., a pediatric hospitalist and member of the BabyCenter Advisory Board. "Unlike cow's milk allergy, lactose intolerance is rare before 3 to 5 years of age unless your child's gut has been temporarily damaged by an illness such as viral gastroenteritis, aka stomach flu. The exception to this is premature babies who haven't quite developed the ability to properly digest lactose yet."
If you think your baby might be allergic to the formula you're giving them, bring it up with your pediatrician. They can help pinpoint what's causing your baby's discomfort.
A cow's milk allergy can be hard to manage, but the good news is most babies outgrow it by about 18 months to 2 years old.
Key takeaways
- A cow's milk allergy is the most common food allergy in children; about 3% of kids under age 3 show symptoms.
- Signs of a cow's milk allergy include vomiting, diarrhea, itchy eyes, hives, and eczema.
- Your baby's pediatrician can help figure out whether your child has a milk allergy or some other issue.
It's not surprising that some of the most common signs of an allergic reaction to formula are gastrointestinal, including:
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Frequent spit up and excessive gassiness may also be signs of a milk allergy.
Not all signs of a formula allergy are gastrointestinal, though. Other signs of an allergy include:
- Itching or tingling of the mouth
- Swelling of the lips, tongue, or throat
- Cough or mild shortness of breath
Your child may also develop itchy raised bumps on the skin known as hives. This is a type of skin rash that often occurs as a result of an allergic reaction. Hives can appear anywhere on the body and may look like tiny spots, blotches, or large bumps.
Another common rash that may appear with a formula allergy is known as eczema (atopic dermatitis) and can cause red, itchy, or dry skin. Eczema tends to show up on the cheeks and scalp in babies but can appear anywhere on the body.
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If you notice that your baby is continually fussy or crying and has obvious signs of discomfort shortly after you've started feeding, talk to your baby's doctor. Babies with milk allergies can show symptoms anywhere from days to weeks after first drinking cow's milk-based formula.
In some cases, a severe food allergy may cause a life-threatening reaction called anaphylaxis. If your baby has any of the following symptoms, call 911 or go to an emergency room immediately:
- Turning blue
- Wheezing
- Trouble breathing
- Facial swelling (including the lips or tongue)
What's the difference between a milk allergy and lactose intolerance?
A milk allergy is an atypical immune response, but lactose intolerance is primarily a digestive issue in which the body doesn't produce enough of the enzyme lactase to properly digest the lactose in milk.
Lactose intolerance can cause diarrhea, bloating, and gas, but it's usually not dangerous. It's more common in adults than in children: If your child does develop this condition, they likely won't start showing signs until they're at least 3 to 5 years old.
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It can be difficult to tell the difference between a milk allergy and lactose intolerance, since both conditions can cause uncomfortable gastrointestinal symptoms. If you have any concerns at all, talk to your baby's pediatrician. They can help figure out whether your baby has a cow's milk allergy, lactose intolerance, or some other issue.
First, check with your child's doctor to make sure that something else isn't causing the reaction. Once they rule out other possibilities, they may recommend a hypoallergenic (hydrolyzed) formula or an amino acid-based formula that's processed to avoid allergic reactions.
Your doctor most likely won't recommend a soy formula – soy is also a highly allergenic food, so if your baby is allergic to milk, they may also be allergic to soy. In fact, about 8 to 14% of babies with a cow's milk allergy will also have a reaction to soy. Ask your baby's doctor before switching to a soy formula.
Based on the severity of your baby's reaction, their doctor may recommend keeping epinephrine auto-injectors on hand in case they accidentally have a milk product and have a severe reaction to it.
