Which is more likely in a baby?
In babies, a reaction to milk is more often an allergy question than an intolerance one. Cows' milk is one of the most common foods to cause allergy in babies, and the AAP notes that milk allergies tend to appear in the first year of life, while lactose intolerance is not very common in infants. All babies are born with lactase, the enzyme that digests milk sugar.
There are exceptions. The AAP explains that some premature babies have a short-lived lactose intolerance (developmental lactase deficiency), that a very rare inherited condition, congenital lactase deficiency, causes severe diarrhoea, and that lactose intolerance can be temporary after a tummy bug. The NHS adds that premature babies who can't digest lactose usually improve as they get older.
Plenty of tummy troubles are neither. Reflux, colic and changes in poo after starting solids are common. The NHS notes that a GP may check for cows' milk allergy because its symptoms can be very similar to reflux.
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).
- Ask for an urgent GP appointment, or call your local urgent advice line (NHS 111 in the UK), if there's blood in your baby's poo, your baby is refusing to feed, or keeps being sick and can't keep fluid down (NHS).
- Get urgent advice too if your baby has diarrhoea lasting over a week or signs of dehydration, such as fewer wet nappies than usual (NHS).
- See your GP if you think your baby may have a milk allergy or lactose intolerance: for example hives after a dairy food that have settled, eczema that flares, tummy symptoms after milk that keep coming back, or a baby who isn't gaining weight.
Cows' milk allergy and lactose intolerance side by side
Drawn from ASCIA (the Australian and New Zealand allergy specialists' body), the AAP and the NHS. The symptoms overlap, so use this to describe what you've seen to a doctor, not to decide at home.
| What to compare | Cows' milk allergy | Lactose intolerance |
|---|---|---|
| What's going on | The immune system reacts to cows' milk protein | The body doesn't make enough lactase, the enzyme that digests lactose (milk sugar) |
| How common in babies | Cows' milk is one of the most common food allergies in babies; ASCIA reports more than 2% of infants in Australia and New Zealand | Not very common in infants; the AAP says it typically starts showing up after age 3 in children born full-term |
| Typical signs | Fast: hives, swelling of the lips, face or eyes, vomiting. Delayed: worsening eczema, vomiting or diarrhoea | Tummy pain, bloating, wind, tummy rumbling, diarrhoea, feeling or being sick |
| When it starts | Fast reactions within minutes to 2 hours; the NHS says cows' milk allergy can take up to 3 days | A few minutes to a few hours after lactose (NHS) |
| Can it be dangerous? | Yes: anaphylaxis can happen and is always a medical emergency | Uncomfortable but not dangerous; no rashes or anaphylaxis (ASCIA) |
| Lactose-free milk or formula | Not suitable: it still contains cows' milk protein (ASCIA) | Only if a doctor or dietitian advises it |
How the two differ
- Allergy is an immune reaction: in cows' milk allergy, the body reacts to milk proteins. ASCIA describes fast reactions within 15 minutes and sometimes up to 2 hours, and delayed reactions 2 or more hours later, such as worsening eczema, delayed vomiting and/or diarrhoea.
- Intolerance is a digestion problem: lactose intolerance happens when the body doesn't make enough lactase to digest lactose (NHS). The AAP says the more lactose a child has, the stronger the symptoms.
- Only allergy can cause hives, swelling or breathing problems: ASCIA says lactose intolerance is uncomfortable but not dangerous and does not cause rashes or anaphylaxis.
- Allergy tests help with one but not the other: skin or blood tests are usually positive in fast milk allergy, usually negative in delayed milk allergy, and negative in lactose intolerance (ASCIA).
- Breastfeeding is still fine if you're lactose intolerant: the AAP says it's perfectly safe and doesn't make your baby more likely to be lactose intolerant.
What to do if you suspect either
Check for emergency signs first
Difficult or noisy breathing, swelling of the tongue or throat, wheeze or persistent cough, a hoarse voice or cry, or a baby who becomes pale and floppy after milk or a dairy food are signs of anaphylaxis (ASCIA). Call your local emergency number straight away. Lactose intolerance does not cause these signs.
Don't change milk or formula on your own
The NHS warns against cutting out a major food such as milk without advice, because your baby may miss out on nutrients, and the AAP asks parents to discuss formula options with their paediatrician before switching. If a dairy food such as yoghurt seemed to cause a reaction, stop that food until you've had advice.
Write down what happened
Note what your baby had (breast milk, formula and its name, any dairy foods), roughly how much, when symptoms started and what they looked like. Photos of rashes or nappies help. The NHS says you may be asked to keep a food and symptoms diary.
See your GP, health visitor or paediatrician
Milk allergy is diagnosed from the history, sometimes with skin or blood tests, or with a doctor-planned trial without cows' milk followed by a planned reintroduction (ASCIA). For suspected lactose intolerance, a doctor may suggest a short lactose-free period or a hydrogen breath test, or check the stools of younger babies (NHS; AAP).
Don't use lactose-free milk for a suspected allergy
Lactose-free formula and milk still contain cows' milk protein. ASCIA lists them as unsuitable for cows' milk allergy, along with goat's and sheep's milk formula, partially hydrolysed (HA) formula and A2 milk. If your baby needs a special formula, your GP or specialist will say which.
Make diet changes only with a plan
If either condition is confirmed, cut foods only as advised. The NHS says not to cut foods out of a child's diet without a GP or dietitian, and ASCIA says babies who need to avoid dairy should be supervised by a dietitian, so they still get enough calcium and protein.
