Cow's milk protein allergy in babies is real, and also over-diagnosed

Cow's milk protein allergy is real, and in some babies it causes real suffering until it is spotted. It is also one of the most over-diagnosed conditions of infancy. Proven allergy affects only about 1 in 100 babies, while crying, spitting up and rashes are common in healthy babies. A short, strict trial without milk, followed by bringing milk back, is how we tell the two apart.

What is cow's milk protein allergy?

Cow's milk protein allergy (CMPA) is when a baby's immune system reacts to the proteins in milk, mainly casein and whey. It is one of the most common food allergies in early childhood.¹

There are two main types:

• Fast (IgE-mediated) allergy: symptoms start within minutes to about 2 hours of having milk. IgE is the allergy antibody that skin and blood tests measure.
• Slow (non-IgE) allergy: symptoms come hours to days later, mostly in the gut and skin. Allergy tests are often negative.²

In a large European study, about a quarter of children with proven milk allergy had no milk allergy antibody in their blood.²

Is milk allergy the same as lactose intolerance?

No. Milk allergy is an immune reaction to milk protein. Lactose intolerance is trouble digesting lactose, the sugar in milk, and it is uncommon in babies.

This difference matters for treatment. Lactose-free formula still contains cow's milk protein, so it does not help a baby with milk allergy. A baby with true milk allergy needs the protein removed or broken down.¹

Breast milk is high in lactose, and breastfed babies thrive on it. Frothy green stools or wind are not proof of lactose intolerance.

How common is milk allergy in babies?

Much less common than many families are told. When diagnosed properly, with a supervised milk challenge, it affects roughly 0.5% to 1% of babies.^2,3

The EuroPrevall study followed more than 12,000 babies across 9 European countries. Milk allergy was suspected in 358 children but confirmed in only 55, an overall rate of 0.54%.²

Older figures of 2 to 3% are still widely quoted,⁴ but studies that confirm allergy with a challenge test find far fewer. In exclusively breastfed babies, milk allergy exists but is uncommon.⁵ We do not yet have good Indian figures.⁶

What are the signs of cow's milk allergy in a baby?

Fast reactions show as hives, redness around the mouth, swelling of the lips or eyes, or vomiting soon after milk. Slow reactions show as gut and skin problems that build up over days.

Fast reactions often happen the first time a breastfed baby is given formula or a taste of dairy. Rarely, they cause wheeze, breathing difficulty or collapse (anaphylaxis).

Slow reactions can include:

• blood and mucus streaks in the stool of a baby who otherwise looks well
• persistent vomiting or diarrhoea
• eczema that does not settle with good skin care
• poor weight gain
• marked distress with feeds

One rarer form, called FPIES, causes repeated heavy vomiting a few hours after a feed, with paleness and floppiness. The gut forms of slow allergy include inflammation of the bowel lining and of the lower bowel (proctocolitis).⁷

Why is milk allergy over-diagnosed?

Because many of its suggested signs, such as crying, spitting up, loose or green stools and mild rashes, are very common in healthy babies.^5,3

A review of 9 milk allergy guidelines found that most suggested thinking of allergy for these everyday symptoms. Yet troublesome crying, vomiting or rashes each affect 15 to 20% of babies, while proven allergy affects about 1%.³ The same review found that 81% of guideline authors had links with formula makers.³

The latest European position paper says plainly that over-diagnosis happens much more often than under-diagnosis, and that both cause harm.⁵ It adds that changes in stool, feeding refusal and the odd spot of blood in the stool are common and do not by themselves prove allergy.⁵

What harm does a wrong diagnosis of milk allergy cause?

Mothers may stop breastfeeding, and babies get costly special formula they do not need.^3,6 Families can also start to see a healthy baby as fragile.

Prescriptions of special formulas for milk allergy have risen sharply. In England in 2020, volumes were about 10 to 13 times higher than expected from the true rate of allergy.⁸ Some of these formulas, especially amino acid types, are also high in sugars.⁸

A paper on allergy care in India describes how, in richer countries, formula marketing widened the boundaries of milk allergy and undermined breastfeeding, and warns India not to repeat this.⁶ Dr Dutta regularly meets mothers who have cut out milk, curd, paneer and every mishti for months, with nobody sure the diagnosis was right.

Can blood in my baby's stool be milk allergy?

Sometimes. A few streaks of blood and mucus in the stool of a well, thriving breastfed baby can be a mild slow milk allergy called allergic proctocolitis.⁷

But an occasional spot of blood alone does not prove allergy.⁵ Small tears around the anus from passing stool are a common, harmless cause. Swallowed blood from a cracked nipple can also show up in the stool.

Always show your doctor. A baby who has blood in the stool and is unwell, feverish, pale, vomiting or has a swollen tummy needs urgent care, because other causes must be ruled out.

How do doctors diagnose cow's milk allergy?

For the slow type, by removing cow's milk protein strictly for 2 to 4 weeks, then bringing it back. If symptoms clearly improve and then return, the diagnosis is confirmed.^5,9

The European paper calls this challenge after a short elimination diet the cornerstone of diagnosis.⁵ It is the only reliable way to diagnose the gut forms of slow milk allergy in babies.⁷

The step most often skipped is putting milk back. If symptoms do not return, your baby probably never had milk allergy and can go back to a normal diet.

For fast allergy, skin prick or blood tests help. Milk challenges should be done under medical supervision.⁹ After a severe reaction or FPIES, never try milk again at home.

Do I need to stop breastfeeding if my baby has milk allergy?

No. Please keep breastfeeding. If a breastfed baby is diagnosed, the usual first step is for the mother to remove cow's milk protein from her own diet.⁹

Only tiny amounts of cow's milk protein pass into breast milk. One analysis estimated that for more than 99% of babies with proven milk allergy, the breast milk of a mother who drinks milk does not contain enough to trigger a reaction.³ This is another reason to be cautious before blaming breast milk.

Do not switch to formula without talking to your doctor.

What should a breastfeeding mother avoid on a dairy-free diet?

All foods made from cow's or buffalo milk, plus packaged foods with milk in the ingredients. In a Kolkata kitchen, that is more than you might expect.

• milk, tea or coffee with milk, curd, dahi, lassi, buttermilk
• paneer, cheese, butter, cream, khoa, malai
• chhena sweets: rasgulla, sandesh, mishti doi, and most other mishti
• biscuits, cakes, bread, chocolates and ready foods that list milk, milk solids, whey or casein on the label

Label reading is a key skill on this diet.¹ Ghee contains very little milk protein, and many dietitians allow it. If your baby's symptoms are severe, ask before keeping it.

Dairy gives many Indian mothers most of their calcium. On this diet you will need a calcium supplement and vitamin D, and a dietitian's help is worth it. Growth and nutrition should be checked regularly in anyone on a milk-free diet.⁹

Can my baby have buffalo or goat milk instead?

No. Other animal milks are not recommended, because most babies allergic to cow's milk react to them too.¹

The proteins in buffalo, goat and sheep milk are very similar to cow's milk protein. They are also not complete foods for babies.¹

Rice drinks and homemade almond milks are not complete foods for babies either. Plant drinks may suit older toddlers who eat well, but only with careful planning.¹

Which formula is best for a baby with milk allergy?

An extensively hydrolysed formula, in which the milk proteins are broken into tiny pieces that most allergic babies do not react to, is the usual first choice.⁹

• Amino acid formula, made from protein building blocks, is kept for babies who react to hydrolysed formula or have severe allergy.⁹ It costs much more.
• Soya formula is generally not advised under 6 months.^9,7
• Partially hydrolysed ("HA") formula and lactose-free formula are not suitable for treating milk allergy.

Hydrolysed formulas taste bitter. Young babies usually accept them more easily than older ones. Give it a few days.

When do babies outgrow cow's milk allergy?

Most do. More than 75% tolerate milk by 3 years, and more than 90% by 6 years.⁹

The slow type usually goes early. In the EuroPrevall study, all children with the slow type tolerated milk one year after diagnosis.² The fast type can last longer. In one US referral clinic, it had resolved in only about 4 in 10 children by age 8, and about 8 in 10 by age 16.⁴

That is why children on a milk-free diet should be rechecked every 6 to 12 months to see whether they have grown out of it.⁹ Overly long restrictions hurt growth and family life.⁹

What is a milk ladder?

A milk ladder is a step-by-step plan to bring milk back, starting with small amounts of milk well baked into foods like a biscuit or cake, then moving to less cooked forms and finally fresh milk.

Heat changes milk proteins, so many allergic children can eat baked milk before they can drink milk. Building tolerance to baked milk is part of good allergy care.¹

The ladder was first used for the slow type of allergy. A recent review found it may also help children with the fast type develop tolerance.¹⁰ For children with fast allergy, the first steps should be planned and supervised by your doctor.

When should I see a doctor about milk allergy?

Call emergency services or go to hospital straight away if, after milk, your baby has:

• swelling of the lips, tongue or face
• noisy breathing, wheeze or difficulty breathing
• repeated vomiting with paleness or floppiness
• collapse

Make an appointment if your baby has blood in the stool, eczema that will not settle, poor weight gain, or distress with most feeds, and before you start any elimination diet. If you have been dairy-free for months with no plan to test milk again, come back so we can check whether the diet is still needed.