Does human breast milk contain lactose?

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Can you breastfeed your baby if they’re lactose intolerant? Get the advice you need from our baby experts.

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If you suspect that your baby could have a lactose intolerance and you’re breastfeeding, you might be wondering: is breast milk lactose-free? The answer is no, it isn’t - human breast milk contains lactose.

While lactose intolerance is very rare in babies, it does happen occasionally. And, despite the lactose in human milk, the best thing for your baby is usually to continue breastfeeding unless advised otherwise by your healthcare professional1.

Read on to learn more about breastfeeding and lactose intolerance.

Lactose in human breast milk

Does breast milk contain lactose? It’s a common breastfeeding question, and the answer is yes. All milk produced by mammals contains lactose - that includes breast milk2.

But what is lactose, and why is it important?

What is lactose?

Lactose is a type of sugar and the main carbohydrate in breast milk1. It’s the most plentiful nutrient that your breast milk contains, with around 7g of lactose per 100ml3.

The importance of lactose for your baby

Lactose plays a big part in your baby’s growth and development. Like all carbohydrates, lactose is a source of energy. For breastfed babies, the lactose in breast milk provides most of the energy they’ll need as they grow2.

Lactose is also thought to help your baby absorb calcium for healthy bones4, feed the good bacteria in their gut5, and support the development of their immune system6. There’s also some research to suggest that lactose may contribute to the development of your baby’s brain7.

Lactose intolerance in babies

The small intestine produces an enzyme called ‘lactase’, which breaks lactose down into 2 sugars known as ‘glucose’ and ‘galactase’. This makes it easier for the body to absorb8. If we don’t have enough lactase in our bodies, then we can’t break down the lactose, which can cause symptoms of lactose intolerance. 

In babies, symptoms of lactose intolerance can include9:

  • Green, watery diarrhoea
  • Excessive wind
  • A bloated tummy

There are four kinds of lactose intolerance; let’s take a look.

Congenital lactose intolerance

Congenital lactose intolerance is very rare and results from a genetic defect. It can occur in both breastfed and formula-fed babies. Newborns with congenital lactose intolerance can experience severe diarrhoea that can be tricky to treat, and they need to have specialised treatment and care to ensure they get the nutrients they need2.

Developmental lactose intolerance

This tends to occur in babies born prematurely, who aren’t able to digest lactose until their gut cells develop properly. This happens at around week 34 of pregnancy. This type of lactose intolerance usually resolves over time as your baby grows and develops2.

Primary lactose intolerance

Primary lactose intolerance is the most common type of lactose intolerance. Babies born at full term are born with the ability to digest the lactose in the milk they drink. Over time, this ability reduces (usually at around 1 year). In cases of primary lactose intolerance, the body’s lactase production falls sharply. Symptoms typically start between the ages of 5 and 6, although they can start earlier in some cases (between the ages of 2 and 3)10, 2.

Most people with primary LI can tolerate some lactose in small doses throughout the day2.

Secondary lactose intolerance

Secondary lactose intolerance occurs when an infection, such as gastroenteritis or norovirus, or a food allergy damages the gut (where lactase is produced). It’s more common in children and usually gets better on its own, once the gut has healed (this can take 1-2 months)2,9.

Is it lactose intolerance or cow’s milk allergy?

Lactose intolerance often gets confused with cow’s milk allergy, but they’re two different things.

Cow’s milk allergy is common in babies and young children. It involves your immune system, and is caused by an allergic reaction to a protein found specifically in cow’s milk11. Lactose intolerance doesn’t involve the immune system and is caused by the body’s inability to digest the sugar in milk (lactase) or the absence of the lactase enzyme12.

Interested in learning more about Cow’s Milk Allergy?

Read now

Can a baby be intolerant to lactose from breast milk?

Yes, babies can be intolerant to lactose in breast milk. However, that doesn’t mean that you’ll need to stop breastfeeding.

Whilst babies with congenital lactose intolerance won’t be able to breastfeed, if your baby has developmental, primary or secondary lactose intolerance, you can continue to breastfeed. If your baby has secondary lactose intolerance, your GP or health visitor will likely advise you to continue breastfeeding9, as any lactose that you eat or drink won’t affect the levels of lactose in your breast milk. As a result, it’s unlikely that you’ll have to restrict your own diet1.

Treating the underlying cause of your baby’s lactose intolerance should mean that symptoms improve without having to stop breastfeeding9.

When to speak to a GP

If you think your baby is having a reaction to your breast milk, it’s important to speak to your GP or health visitor. They’ll likely ask you questions about your baby’s symptoms to better understand what might be causing them – whether that’s lactose intolerance, a cow’s milk allergy, or something else.

Your GP will also be able to give you advice about managing your baby’s symptoms while making sure they still get all the nutrients they need as they develop and grow.

  1. Australian Breastfeeding Association (2022). Lactose intolerance and the breastfed baby [online]. Available at https://www.breastfeeding.asn.au/resources/lactose-intolerance-and-breastfed-baby [Accessed July 2025]
  2. Heine RG, AlRefaee F, Bachina P, De Leon JC, Geng L, Gong S, Madrazo JA, Ngamphaiboon J, Ong C, Rogacion JM. Lactose intolerance and gastrointestinal cow's milk allergy in infants and children - common misconceptions revisited. World Allergy Organ J. 2017 Dec 12;10(1):41. doi: 10.1186/s40413-017-0173-0. PMID: 29270244; PMCID: PMC5726035.
  3. Infant and Young Child Feeding: Model Chapter for Textbooks for Medical Students and Allied Health Professionals. Geneva: World Health Organization; 2009. SESSION 2, The physiological basis of breastfeeding. Available from: https://www.ncbi.nlm.nih.gov/books/NBK148970/
  4. Abrams SA, Griffin IJ, Davila PM. Calcium and zinc absorption from lactose-containing and lactose-free infant formulas. Am J Clin Nutr. 2002;76:442–446. doi: 10.1093/ajcn/76.2.442.
  5. Francavilla R, Calasso M, Calace L, Siragusa S, Ndagijimana M, Vernocchi P, Brunetti L, Mancino G, Tedeschi G, Guerzoni E, Indrio F, Laghi L, Miniello VL, Gobbetti M, De Angelis M. Effect of lactose on gut microbiota and metabolome of infants with cow's milk allergy. Pediatr Allergy Immunol. 2012;23:420–427. doi: 10.1111/j.1399-3038.2012.01286.x.
  6. West CE, Renz H, Jenmalm MC, Kozyrskyj AL, Allen KJ, Vuillermin P, Prescott SL, in-FLAME Microbiome Interest Group. The gut microbiota and inflammatory noncommunicable diseases: associations and potentials for gut microbiota therapies. J Allergy Clin Immunol 2015;135:3–13.
  7. Chiurazzi, M.; Cozzolino, M.; Reinelt, T.; Nguyen, T.D.; Elke Chie, S.; Natalucci, G.; Miletta, M.C. Human Milk and Brain Development in Infants. Reprod. Med. 2021, 2, 107-117. https://doi.org/10.3390/reprodmed2020011
  8. InformedHealth.org [Internet]. Cologne, Germany: Institute for Quality and Efficiency in Health Care (IQWiG); 2006-. Lactose intolerance: Learn More – Causes and diagnosis of lactose intolerance. [Updated 2024 Nov 20]. Available from: https://www.ncbi.nlm.nih.gov/books/NBK310263/
  9. NHS South West London. Secondary lactose intolerance [online]. Available at https://swlimo.southwestlondon.icb.nhs.uk/clinical-guidance/nutrition-and-blood/nutrition/speci/secondary-lactose-intolerance/ [Accessed July 2025]
  10. Darma A, Sumitro KR, Jo J, Sitorus N. Lactose Intolerance versus Cow's Milk Allergy in Infants: A Clinical Dilemma. Nutrients. 2024 Jan 31;16(3):414. doi: 10.3390/nu16030414. PMID: 38337698; PMCID: PMC10856892.
  11. NHS County Durham and Darlington (2019). Cow's milk protein allergy (CMPA) [online]. Available at https://www.cddft.nhs.uk/services/nutrition-dietetics/children/allergies-food-exclusions/CMPA [Accessed July 2025]
  12. NHS. Dairy and alternatives in your diet [online 2023]. Available at https://www.nhs.uk/live-well/eat-well/food-types/milk-and-dairy-nutrition/#:~:text=Lactose%20intolerance%20is%20a%20common,does%20not%20cause%20severe%20reactions. [Accessed December 2025]

Last reviewed: March 2026
Reviewed by Nutricia’s Medical and Scientific Affairs Team

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