Cow's Milk Protein Allergy Symptoms in Babies

Ours was the mild, slow kind, which is the kind that hides. There were no hives and nothing dramatic at the table. What we had was eczema that came and went: rough patches on both cheeks, and a matching patch behind each knee that flared for a few days and then settled. We blamed the weather, the washing powder, teething, and the hot water in the bath. What we were actually looking at was a one to two day gap between yoghurt or cheese and the flare, and a gap that long is invisible when you are running on four hours of sleep and going by memory. It only became a pattern once we had a written record with dates next to it. Our paediatrician looked at six weeks of that log and recognised it in about a minute. She also told us what the log could not tell us, which is anything about severity or what to do next. That part was hers to decide.

This is the one most parents picture when they hear the word allergy, and it is the easier one to spot because the timing is obvious. According to ASCIA's cow's milk allergy FAQ, rapid-onset reactions can start within 15 minutes and sometimes up to two hours after cow's milk or other dairy: hives or welts on the skin, swelling of the lips, face or eyes, tummy pain, vomiting, and diarrhoea. The severe version, anaphylaxis, looks different again: noisy breathing or wheeze, swelling or tightness in the throat, or a baby who goes pale and floppy. That is not a moment for a food log. If your baby has any trouble breathing, goes floppy, or their face or throat swells, call emergency services straight away, and give adrenaline first if your doctor has prescribed an injector. Write the details down afterwards, when everyone is safe. Reactions this fast usually show up on skin-prick or blood testing, which is what makes them IgE-mediated.

The delayed kind is not a milder version of the same thing, it works by a different mechanism, and standard allergy tests are usually negative for it. ASCIA puts delayed reactions at two or more hours after dairy, and the NHS guidance on food allergies in babies notes that with cow's milk allergy specifically, symptoms can take up to three days to appear. What parents tend to describe is a gradual mess rather than an event: eczema that will not settle, reflux and posseting, crying that gets filed under colic, loose or mucousy stools, streaks of blood in the nappy, refusing feeds, or weight gain that has slowed. The iMAP guideline, Venter 2017 was written for GPs facing exactly this presentation, because it is the version that gets missed for months. None of these symptoms on its own means milk. Several of them together, tied to dairy by timing, is the thing a doctor can work with.

That is the honest difficulty. Babies cry, posset, have strange nappies, and go through eczema flares without any food being to blame. Every symptom on the delayed list is also a normal Tuesday. The only thing that separates a pattern from a coincidence is timing you can check later, and memory is no good at that, particularly memory this tired. We wrote down the food, the form it was in (yoghurt, cheese, milk in a sauce, or baked into a muffin), roughly how much, and the time. Then, separately, the symptom, where on the body it was, and the time it started. We photographed rashes in daylight, because by the appointment they had faded. The same habit is what makes delayed eczema flares readable at all, and it is the whole of what we handed over at the appointment: dates, times and photos, not a theory. How we set the log up for the paediatrician goes through it in more detail.

The two get used as if they mean the same thing, and they do not. Milk allergy is a reaction to the protein in milk and involves the immune system. Lactose intolerance is a difficulty digesting the sugar in milk, with no immune system involved at all. The NHS page on lactose intolerance describes it as uncommon as a lifelong condition in babies, and when it does show up in an infant it is often temporary, after a bout of gastroenteritis. The symptoms overlap enough to confuse anyone (wind, loose stools, tummy pain), but the diagnosis and the management are different, and so is what it means for the years ahead. We have written up the difference between dairy allergy and lactose intolerance separately, because getting the two mixed up is what sends families down the wrong path for months.

Cow's milk protein allergy can happen in an exclusively breastfed baby, through milk protein in the breastfeeding parent's own diet, so a baby who has never had dairy directly is not automatically ruled out. What we did not do was cut dairy out on our own to test the theory. The NHS is blunt about experimenting with removing a major food from a child's diet without advice, and ASCIA says exclusion and reintroduction should be supervised, because a trial exclusion only means something if a planned reintroduction follows it. Our paediatrician set the timing and a dietitian checked the nutrition. If milk allergy is confirmed, reintroduction later often follows a staged plan, which we have covered in the milk ladder explainer. And if it turns out milk is not the problem, dairy stays in the diet, which is where introducing dairy picks up. Most children outgrow cow's milk allergy by three to five years of age.