Is my baby lactose-intolerant?
Lactose is a mammalian sugar and the reason infants love the taste of breast milk so much.
It is extremely rare for infants to be born lactase-deficient, so nearly all babies should be able to tolerate lactose.
A common cause of lactose intolerance is transient intolerance, which occurs for a short period after diarrhoea, illness, or a course of antibiotics.
Severe chronic illness affecting the GIT can also cause this.
Lactase non-persistence (which occurs in much of the world) only comes on with increasing age, not in infancy.
Symptoms and Signs of Lactose Intolerance in Infants
Lactose intolerance in infants typically presents with the following classic symptoms:
Watery, acidic diarrhoea
- Abdominal distension
- Flatulence
In severe cases, continued intake of lactose-containing feeds can lead to failure to thrive and dehydration. It's important to note that hives, immediate-onset rashes, and tissue swelling are signs of Cow's Milk Protein Allergy (CMPA), not lactose intolerance.
Symptoms usually appear after the ingestion of breast milk or standard infant formula, both of which contain lactose.
In cases of congenital lactase deficiency (alactasia), which is extremely rare, symptoms emerge shortly after feeding begins, resulting in persistent diarrhoea that can cause weight loss and severe dehydration.
Secondary lactose intolerance, which occurs more frequently (e.g., after infections or mucosal injury), presents with similar symptoms but may be less severe and often transient. Symptoms can include abdominal pain, bloating, and increased stool frequency. The onset of these symptoms is closely linked to lactose intake and typically resolves with the elimination of lactose from the diet.
For infants who develop lactose intolerance, numerous lactose-free formula options are available, including rice- and soy-based formulas.
Although breast milk contains lactose, there is no need to discontinue it, as transient lactose intolerance usually resolves on its own.
Our team is experienced in guiding you through a potentially challenging diagnostic process. For a more comprehensive evaluation of non-IgE adverse reactions, please refer to the EAACI guidelines titled "Diagnosis and Management of Non-IgE Gastrointestinal Allergies in Breastfed Infants" - an EAACI Position Paper, in which Prof. Du Toit participated.
Frequently Asked Questions
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Human milk has the highest lactose concentration, typically around 6.7–7.0 g per 100 mL (67–70 g/L).
In comparison, cow's milk has a lower lactose content, averaging about 4.6–4.9 g per 100 mL (or 46–49 g/L).
Most infant formulas in the United Kingdom are designed to mimic human milk (a hard task), and their lactose content is generally similar to or slightly lower than that of human milk, typically ranging from 4.5 to 7 g per 100 mL (45–70 g/L), depending on the brand and formulation.
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We make us of clinical history, dietary elimination-and-rechallenge, expecting resolution of symptoms with lactose elimination and recurrence with reintroduction supports the diagnosis. In infants where formal testing is difficult.
Hydrogen breath test (HBT) is the most widely used and recommended non-invasive diagnostic method for lactose intolerance in older children. It involves administering an oral lactose load (typically 1–2 g/kg, up to a maximum of 25 g) and measuring breath hydrogen at intervals. An increase in breath hydrogen ≥20 ppm above baseline is considered diagnostic for lactose malabsorption. The test is interpreted in conjunction with the presence of symptoms during or after the test, as symptom correlation is essential for diagnosing lactose intolerance rather than just malabsorption.
Symptom assessment after lactose challenge is critical. Validated symptom questionnaires or direct observation of symptoms (such as diarrhea, abdominal pain, bloating, or flatulence) following a lactose load are used to confirm clinical intolerance, as malabsorption and symptoms do not always correlate.
Genetic testing for lactase non-persistence (C/T-13910 polymorphism) may be considered, especially in populations with a high prevalence of lactase persistence or in cases where the breath test is not feasible. - However, genetic testing identifies predisposition to primary lactase deficiency but does not confirm current intolerance or secondary causes, which are more common in infants.
Stool acidity and reducing substances may be used as supportive tests in infants, especially when breath testing is not feasible. Acidic stools (pH <5.5) and the presence of reducing substances suggest carbohydrate malabsorption but are not specific for lactose.
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Ethnic groups worldwide at increased risk for developing lactose intolerance include: East Asian, West African, Arab, Jewish, Greek, Italian, Hispanic/Latino, Native American, and most Indigenous Australian and Pacific Islander populations.
In these groups, the prevalence of lactase non-persistence (and thus lactose intolerance) ranges from 70% to nearly 100% in adulthood, with the highest rates observed in East Asian and Native American populations.
In contrast, Northern Europeans (e.g., Scandinavian, British, Irish) have the lowest prevalence of lactose intolerance, with lactase persistence rates exceeding 90% in some populations.
Lactose intolerance, if it does develop, in at risk populations, usually presents after age 5yr, as lactase enzyme activity begins to decline following weaning.
The onset of symptoms is most common in mid-childhood to adolescence, although the exact age can vary depending on genetic background.
In populations with high rates of lactase non-persistence, the decline in lactase activity and the emergence of symptoms may occur as early as 5–7 years of age.
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Breastfeeding should be continued wherever possible, as human milk is generally well tolerated except in the exceptionally rare cases of congenital lactase deficiency.
For lactose intolerant infants, the recommended infant formulas are rice or soy-based infant formulae, or lactose-free cow’s milk protein-based formulas.
Lactose-free formulas are generally nutritionally complete and use alternative carbohydrates such as glucose polymers or corn syrup solids instead of lactose. These formulas are appropriate for infants with congenital lactase deficiency or secondary lactose intolerance (e.g., post-gastroenteritis) who are not breastfed and do not have cow’s milk protein allergy.
Soy-based formulas are not recommended as first-line for ex-prem infants under 6 months due to concerns about phytoestrogen exposure.
Avoid Soy milks if there is a coexisting soy allergy.
Extensively hydrolyzed or amino acid-based formulas are not indicated for isolated lactose intolerance but are reserved for infants with severe cow’s milk protein allergy.
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