Infant Milk Allergy, Lactose Intolerance, or Something Else?

Medically Reviewed by Dan Brennan, MD on December 06, 2022
5 min read

If your baby seems to react badly to infant formula milk, you're probably wondering why it's happening. Maybe you think it's a cows' milk allergy, milk protein intolerance, or lactose intolerance.  

Lots of people think those problems are the same, but they’re not. Some of the symptoms they cause may be similar, so it can be confusing. Or it might not be any of those things. Your pediatrician will help you work out what's going on.

Some infants seem to have difficulty digesting their milk. They may be fussy, spit up or have green stools with mucus and small flecks of blood.

These tummy troubles are often caused by an intolerance to cows’ milk protein. This sensitivity is different from a true allergy to cows’ milk. Babies may ingest cows’ milk protein from a standard formula or through breast milk, if mom is consuming products that contain cows’ milk protein. About half of infants with milk protein intolerance will also have difficulties digesting soy protein as well.
It turns out that cows’ milk protein intolerance is more common than a true allergy to cows’ milk. 

Most infant formula milk is made from cows' milk. The first time a baby has cows' milk, it's very likely to be in formula. That's because cows' milk itself isn't recommended as a drink for children under the age of 1. But from around 6 months old, when a baby is being introduced to solids, they can have cows’ milk as an ingredient in foods.

Cows' milk allergy is one of the most common allergies for babies and young children. Experts estimate that 2% to 7.5% of babies under 12 months old have it. If it happens, your child's immune system reacts to the proteins in milk, triggering allergy symptoms. That's why it's sometimes called cows' milk protein allergy.

Sometimes, babies who are breastfed can have this allergy. It's because the cows' milk from the mom's diet is being passed on to the baby through their breast milk.

Most children grow out of the allergy by the time they reach the age of 5. 

Your child may have symptoms within minutes of having cows' milk or formula made from it. In other cases, problems might not happen until hours or even days afterward.

There are lots of possible symptoms:

  • Digestion problems, including tummyache, being sick, diarrhea, and constipation
  • Skin reactions, such as swelling of the lips, face, and eye area, and a red, itchy rash
  • Hay-fever-like symptoms, such as a runny nose and watery eyes
  • Eczema that doesn't get better with treatment

Sudden, severe symptoms are rare but can include swelling of the mouth or throat, wheezing, shortness of breath, and difficulty breathing -- a severe allergic reaction called anaphylaxis, which can also make your child feel faint or become unconscious. This is a medical emergency that requires calling 911 or going to the emergency room immediately.

If your baby is found to have milk protein intolerance or be allergic to cows' milk, your pediatrician or allergy specialist will explain to you how to manage it. 

This will include removing all cows’ milk products from your child’s diet or from mom’s diet if she is breastfeeding. Your pediatrician may also prescribe a special infant formula that doesn't contain cows' milk for bottle-fed babies.

Your doctor will help you work out the best diet for your child at whatever stage they are at and closely follow your child's progress. Your doctor will suggest reintroducing milk after a while to see if your child has grown out of their allergy.

Your child may have a different type of reaction to cows' milk, or formula made from it, called lactose intolerance. This is when their body can't digest lactose, which is a type of natural sugar found in milk.

Lactose intolerance is very uncommon in babies, but becomes more common as we get older. About 70% of people in the world have lactose intolerance. It's more common among people from Asian, African, and Hispanic ethnic groups.

Babies and young children can also become temporarily intolerant to lactose after they've had a tummy bug or another condition.

Some of the symptoms of being intolerant to lactose are similar to those of a milk protein intolerance and cows' milk allergy. 

These may include digestion problems such as tummy aches, bloating, diarrhea, and gas. 

Your pediatrician can often determine if your child is lactose intolerant by removing lactose from your child’s diet. This can be accomplished by temporarily substituting lactose-free dairy or soy products.

If the lactose elimination test improves your child’s symptoms, then your doctor will give you advice on what foods and drinks are suitable. Babies and young children need to get the right nutrients to make sure they grow and develop properly.

For bottle-fed babies with lactose intolerance, your doctor will probably advise you to switch to a lactose-free formula milk.

Lactose intolerance is often only temporary for many babies and young children. Their symptoms will often get better within a few weeks. At this point, it's safe to start gradually bringing milk and dairy back into their diet.

If your baby or small child doesn't handle formula milk very well, it may be something else altogether.

Some of the symptoms of lactose intolerance, milk protein intolerance and cows’ milk allergy are common in babies for other reasons, so it can be tricky to work out what's causing the problem.

It may be reflux. This is when your baby brings milk back up during or after a feed. Most babies bring milk back up sometimes, but for some babies, it can happen a lot and be painful. It can cause them to arch while feeding, make them feel uncomfortable, and make it harder for them to feed and gain weight.

It may be colic. This is when the baby cries a lot and you can't work out why. Colic can make babies fussy and gassy, which can also be symptoms of an allergy or intolerance to milk.

If your baby or child is having any problems with feeding, isn't putting on weight, or is showing any other symptoms you are concerned about, talk to your pediatrician. They can help figure out what the problem is and how to fix it.