How common is milk allergy, and what else could it be?
Cows' milk is one of the most common foods to cause allergy in babies. ASCIA reports that more than 2% (1 in 50) of infants in Australia and New Zealand are allergic to cows' milk protein. It can show up in formula-fed babies, in breastfed babies, or when dairy foods such as yoghurt are first offered with solids.
Several everyday baby problems look similar. Reflux, where a baby brings up milk during or after feeds, is very common and usually gets better on its own; the NHS notes that a doctor may check for cows' milk allergy because the symptoms can be very similar. Lactose intolerance is different again: it's a problem digesting milk sugar, not an immune reaction, and ASCIA notes it does not cause rashes or anaphylaxis.
Many children grow out of it. ASCIA says most children outgrow cows' milk allergy by three to five years of age, though it can remain lifelong, and the NHS also notes that lots of children outgrow milk allergy. Whether and when to test that is a decision for your doctor or allergy team.
When to get help
- Call your local emergency number straight away if your baby has any one of these signs of anaphylaxis, as listed by ASCIA: difficult or noisy breathing; swelling of tongue; swelling or tightness in throat; wheeze or persistent cough; difficulty talking or hoarse voice; persistent dizziness or collapse; pale and floppy (in young children).
- The NHS also says to call 999 (in the UK) if a child is limp, floppy or not responding like they normally do. If your baby has a prescribed adrenaline auto-injector, use it, then call for an ambulance even if they seem better.
- Get urgent medical help for repeated vomiting that starts a few hours after a feed or food, especially with pallor, unusual sleepiness or floppiness. This can be FPIES or another serious illness.
- Ask for an urgent GP appointment (or call NHS 111 in the UK) if there is blood in your baby's poo, as the NHS advises.
- See your GP if you think your baby may have a milk allergy, for example hives or swelling after a dairy food that has settled, eczema that flares after feeds, ongoing diarrhoea or vomiting, or poor weight gain.
Fast and delayed milk allergy
ASCIA, the Australian and New Zealand allergy specialists' body, describes two main patterns. Plenty of babies don't fit neatly into either, so take what you've seen to a doctor rather than sorting it out at home.
| What to compare | Fast reactions (IgE-mediated) | Delayed reactions (non-IgE-mediated) |
|---|---|---|
| When it starts | Within 15 minutes and sometimes up to 2 hours after milk or dairy | Usually 2 or more hours after; the NHS says up to 3 days for cows' milk allergy |
| Common signs | Swelling of lips, face or eyes, hives or welts, tummy pain, vomiting, diarrhoea | Worsening eczema, delayed vomiting and/or diarrhoea |
| Allergy tests | Skin or blood tests for IgE are usually positive | Allergy tests are usually negative |
| How it's confirmed | Medical history and allergy tests, with a specialist | A doctor-planned trial without cows' milk, then a planned reintroduction |
| Emergency risk | Anaphylaxis can happen and is always a medical emergency | FPIES, a less common delayed type, can cause repeated vomiting, pallor and floppiness and needs urgent care |
Why milk allergy happens and how it shows up
- The immune system reacts to the protein in cows' milk as though it were harmful. That's what makes it an allergy rather than lactose intolerance, which ASCIA explains is caused by a lack of the enzyme that digests milk sugar.
- In fast (IgE-mediated) allergy, the body has made IgE antibodies to milk protein. ASCIA says reactions can start within 15 minutes and sometimes up to two hours after milk, and skin or blood allergy tests are usually positive.
- In delayed (non-IgE-mediated) allergy, ASCIA says symptoms usually start two or more hours after milk and may include an increase in eczema, delayed vomiting and/or diarrhoea. Allergy tests are usually negative, which is why diagnosis relies on a supervised trial without milk.
- FPIES (food protein-induced enterocolitis syndrome) is a less common delayed type. The international FPIES guideline published with the AAAAI describes repetitive vomiting that starts about 1 to 4 hours after the food, often with lethargy and pallor, and lists cows' milk among the most commonly reported triggers.
- Blood in the poo can be one sign. The AAP describes allergic colitis caused by cows' milk protein, including in healthy babies with rectal bleeding. Blood in a baby's poo has other causes too, and the NHS lists it as a reason for an urgent GP appointment.
- Some babies are more likely to have food allergies: the NHS says to take particular care, and talk to your GP or health visitor first, if your baby has eczema or a diagnosed food allergy, or there's a family history of food allergies, eczema, asthma or hay fever.
What to do if you think your baby has a milk allergy
If you see signs of anaphylaxis, call for help first
If your baby has any one of ASCIA's signs of anaphylaxis (difficult or noisy breathing, swelling of tongue, swelling or tightness in throat, wheeze or persistent cough, difficulty talking or hoarse voice, persistent dizziness or collapse, or pale and floppy), call your local emergency number straight away. If your baby has a prescribed adrenaline auto-injector, use it as their action plan says, then call, even if they seem better.
Stop the dairy food that seemed to cause it
If a reaction followed a dairy food such as yoghurt or cheese, stop giving that food and get medical advice. ASCIA advises seeking specialist medical advice before offering a food again after signs of an allergic reaction.
Don't swap formula or cut dairy on your own
The NHS warns against experimenting by cutting out a major food such as milk, because your child may not get the nutrients they need, and the AAP asks parents to discuss formula options with their paediatrician before switching. ASCIA lists lactose-free, goat's or sheep's milk, partially hydrolysed (HA) and A2 formulas or milks as unsuitable for cows' milk allergy, so a supermarket swap can make things worse rather than better. Keep feeding as usual until you've had advice.
Write down what happened
Note what your baby had (breast milk, formula and its name, any dairy foods), when, roughly how much, what you saw and how long after the feed it started. Photos of rashes or nappies help. The NHS says you may be asked to keep a food and symptoms diary.
Get a diagnosis from a professional
See your GP or paediatrician. For fast reactions, a doctor can confirm the allergy with your baby's history and skin prick or blood tests. For delayed reactions, ASCIA says diagnosis usually involves removing cows' milk for a trial period of one to four weeks and then a planned reintroduction, guided by a specialist. ASCIA also says there is no place for unproven tests such as IgG food testing, kinesiology or hair analysis.
If it's confirmed, follow the plan you're given
Your doctor will say which formula is suitable, or whether a breastfeeding parent needs to change their diet. ASCIA says this is rarely required and should be supervised by a dietitian, and that babies with cows' milk allergy should also see an allergy dietitian and have an action plan for reactions. Read food labels for milk. Don't try milk again at home, including baked milk in muffins or biscuits, unless your allergy team has said it's suitable for your baby.
