Baby lactose intolerance: how to tell it from cow's milk allergy, and what to do

You may be worried about baby lactose intolerance, but Families for Life says the kind a baby is born with is extremely rare. The kind you're more likely to see comes after a tummy bug, lasts a few weeks and settles as the gut heals. The same wind, fussing and runny poo can also come from cow's milk allergy, or show up in a healthy baby. Keep feeding as you are, and let your doctor decide whether the milk needs to change.

What to do if you think your baby is lactose intolerant, step by step

1. Keep feeding your baby. SingHealth says breastfed babies with diarrhoea should keep breastfeeding and feed more often, and formula-fed babies stay on their usual formula.
2. Leave the milk as it is for now. Families for Life says to check with your GP or a registered dietitian before you use or switch to a low-lactose or lactose-free formula.
3. Write down each feed and nappy, plus any wind, rash or long crying spells. Our feed and nappy log does the job, and a photo of an odd nappy helps the doctor.
4. Check for signs that point to allergy instead. Families for Life says vomiting, blood or mucus in the poo, hives and swelling around the eyes aren't signs of lactose intolerance, so take these to a doctor.
5. Watch for dehydration while the diarrhoea lasts. SingHealth lists not passing urine, weight loss, tiredness and a dry tongue, eyes and lips; get your baby seen the same day if you spot them.
6. Protect a sore bottom. Families for Life says acidic poo can leave a red, raw nappy rash, and suggests a good protective cream.
7. Book a GP or polyclinic visit if the diarrhoea isn't getting better. For a baby under 3 months who seems unwell, KKH advises the Children's Emergency instead.
8. Tell your helper and the grandparents the plan. Ask them not to swap the milk or skip feeds without checking with you first.
9. Know the urgent signs. Blood in the poo, a baby who can't keep milk down, or breathing trouble after milk need care fast, and the list is further down this page.

Lactose intolerance vs cow's milk allergy at a glance

The two get mixed up all the time, but they're different problems. KKH explains that lactose intolerance is a shortage of lactase, the enzyme that breaks down lactose, the main sugar in milk. In cow's milk allergy the trouble is milk protein, not lactose. Here's how KKH, SGH, Families for Life and Cambridge University Hospitals in the UK describe each one.

Timing alone won't settle it. Cambridge University Hospitals notes that milk allergy can cause delayed signs too, such as diarrhoea, vomiting or blood in the stool. That's why the diagnosis belongs to your doctor. For the full list of reaction signs, see our guide to child allergy symptoms. If a milk allergy is confirmed, KKH says dietitians help families keep a child growing well, and our allergy-friendly eating guide covers food at home and out.

The two kinds of lactose intolerance in babies

Families for Life says lactose makes up around 7% of breast milk and formula, gives a baby around 40% of their energy, and helps them absorb calcium and iron. So cutting it out is a doctor's decision.

Primary lactose intolerance means a baby is born making no lactase at all. Families for Life calls it extremely rare, with severe diarrhoea from the first day of life. SGH says these babies need a lactose-free formula, because they can't digest the lactose in breast milk either.

Secondary lactose intolerance is the temporary kind. A stomach bug such as gastroenteritis irritates the gut lining, and lactase runs short for a while. SGH says a viral or bacterial infection can cause this in children, and that it can last from a few days to a couple of weeks. For home care during the bug itself, see our guide to food poisoning in children.

A third pattern starts later. Families for Life says a child's lactase can run low after the age of 3, sometimes for life, and that people from Asia and Africa are more likely to get it. SGH calls lactose intolerance the most common food intolerance in Asians.

Lactose overload: a breastfeeding pattern that looks the same

Families for Life describes lactose overload separately. Your baby makes lactase as normal, but takes in more lactose at one go than they can break down. It can happen with an oversupply in the early weeks, with a pattern of short feeds, or when your baby switches sides before the first breast is drained. The lactose-rich first milk moves through faster than the later milk.

Here the change is in how you feed. Families for Life suggests making sure your baby gets all the milk from each breast. A lactation consultant can watch a feed with you, and our breastfeeding support guide lists where to find one. If long crying spells are the main worry, our colic and reflux guide covers those, and the baby poop guide explains colours and textures.

Lactose-free formula, breast milk and dairy later on

A lactose-free formula is your doctor's call. SingHealth's advice on baby diarrhoea only raises it when the diarrhoea goes on for more than 10 days, and that's the point to see your doctor. Families for Life says to ask your GP or a registered dietitian before you start or switch, and to avoid soy-based formula under 6 months. For making up any formula, see how to prepare formula safely.

If you breastfeed, Families for Life says you can usually carry on through secondary lactose intolerance, and weaning isn't usually recommended. It adds that a small amount of lactose, built up slowly, can help your baby's gut make more lactase again. Ask your GP before trying lactase drops in expressed milk, as Families for Life notes there's some debate about whether they work.

For an older baby on solids, or a toddler your doctor has diagnosed, KKH suggests small amounts of milk at a time, served with food, and building up slowly. Some children find yoghurt and hard cheeses easier. Check labels for hidden lactose such as whey, curds and milk solids. Our guide on when toddlers can drink cow's milk covers the switch from formula.

When to see a doctor

Most of this can wait for your GP or polyclinic. KKH says a family or polyclinic doctor can see a baby who is feeding well and keeping fluids down, and can refer you on for problems like poor weight gain. Go sooner for these:

• Blood in the poo or vomit, or green vomit. KKH lists these for the Children's Emergency.
• Poor feeding, or vomiting so often your baby can't keep milk down (KKH).
• Any illness in a baby under 3 months old (KKH).
• Signs of dehydration: no wet nappies, a dry tongue, eyes and lips, or unusual tiredness (SingHealth).
• Slow weight gain. Families for Life lists it as a possible sign, and KKH says your family doctor can see it and refer you. Our growth percentile calculator helps you track it between visits.
• Hives or a swollen face, eyes or lips after milk. KKH lists these as signs of an allergic reaction, and Families for Life says to see your GP.
• Trouble breathing, noisy breathing, a hoarse voice, a swollen tongue, or a baby who turns pale, floppy or suddenly sleepy after milk. KKH lists these as signs of a severe allergic reaction: call 995.

Take your baby to KKH or NUH Children's Emergency for the urgent signs, and call 995 for breathing trouble or a baby you can't wake. For questions about diarrhoea or vomiting that aren't an emergency, KKH runs an online pilot, the Urgent Paediatric Advice Line, available from 8.00am to 11.00pm daily (KKH, read 6 Nov 2026). To find a children's doctor near you, use our paediatrician map.

Frequently asked questions

How do I know if my baby is lactose intolerant?

You can't tell at home, because the signs overlap with normal baby fussing and with milk allergy. Families for Life says doctors may use a hydrogen breath test, or take lactose out of the diet for a while, under their guidance, to see if things improve. Bring your feed and nappy notes so the doctor can see the pattern.

Lactose intolerance vs cow's milk allergy: which is more serious?

Cow's milk allergy. KKH says an intolerance causes discomfort but isn't life-threatening, while a food allergy can be. Hives, facial swelling or blood in the poo need a doctor, and breathing trouble needs 995.

Should I switch my baby to lactose-free formula?

Not on your own. Families for Life says to talk to your GP or a registered dietitian before using or changing to a low-lactose or lactose-free formula. If it turns out to be milk allergy, lactose-free formula won't help, because Cambridge University Hospitals notes it still contains milk protein.

Can I keep breastfeeding if my baby is lactose intolerant?

Usually, yes. Families for Life says a breastfed baby with lactose intolerance after a stomach bug can keep breastfeeding, and weaning isn't usually recommended. The rare babies born without lactase are the exception, and SGH says they need a lactose-free formula.

How long does lactose intolerance in babies last after a stomach bug?

Usually not long. SGH says it can last from a few days to a couple of weeks, and Families for Life says it usually improves after a few weeks. If loose poo drags on, or your baby isn't gaining weight, see your doctor.

Is lactose intolerance common in Asian children?

In older children and adults, yes. SGH calls it the most common food intolerance in Asians, and Families for Life says this kind usually develops after age 3. In young babies, it mostly shows up for a short time after a stomach bug.