Milk Allergy vs Intolerance in Babies: How to Tell the Difference
If baby is often irritable, and also displays signs of tummy troubles, milk allergy and intolerance is often suspected as the cause. Breastfeeding mothers restrict their diets and formula-fed babies' formula is switched... often multiple times. Understanding the difference between allergy and intolerance could spare your baby from a trial and error process as you try to pinpoint the cause.
- Milk allergy and milk intolerance are different conditions with different causes and management
- Digestive symptoms alone do not always indicate allergy or intolerance
- Lactose overload is common in young babies and is often mistaken for allergy or intolerance
- Unnecessary dietary restriction or formula changes can disrupt feeding and breastfeeding
- Careful assessment helps avoid trial-and-error approaches
Allergy or intolerance?
There are several digestive disorders related to milk. The most common include:
- Lactose overload
- Lactose intolerance
- Cow's milk protein intolerance (CMPI)
- Milk and soy protein intolerance (MSPI)
- Cow’s milk protein allergy (CMPA)
The terms ‘allergy’ and ‘intolerance’ are often used interchangeably, but they not the same. The cause and treatment differs.
It can be difficult to tell these disorders apart because some physical signs will be the same for all of these disorders, as are behavioral symptoms such as irritability and wakefulness. However, there are usually signs that vary.
Lactose overload (also called transient lactase insufficiency) is a feeding management problem and not a digestive disorder. The reason for inclusion in this article is because the GI symptoms linked to lactose overload are often mistakenly attributed to digestive disorders such as lactose intolerance and milk protein allergy or milk protein intolerance (and also colic and reflux).
Breastfed babies
While it is possible for a breastfed baby to have an allergic reaction or experience intolerance to cows’ milk protein or other food proteins eaten by his mother and transferred into her milk, the risk is significantly lower compared to formula-fed babies who receive cows’ or goats' milk-based infant formula and other food proteins such as soy directly. The protein in breastmilk is softer, more easily digestible compared to proteins used in the production of infant formula. Breastmilk also contains digestive enzymes that help a baby to digest the protein within breastmilk.
Consider how milk or food proteins might enter breastmilk. Protein eaten by the mother is broken down into protein molecules in her stomach and digestive tract before it is absorbed to her blood stream. (If food proteins are not broken down into smaller protein molecules in the digestive tract, they are usually too large to be absorbed in the blood stream, and will be passed through the mother’s digestive tract. An exception may be if the mother has ‘leaky gut’). Nutrients in the mother’s blood stream are first filtered by her liver and then face a further filtration system within the mother’s breasts. This complex and highly sophisticated biological process produces milk with a low risk of containing allergens and even lower risk of containing food proteins linked to intolerance.
Note: Around 2/3 of healthy breastfed babies under the age of 3 months at some point experience gastro-intestinal symptoms linked to lactose overload. The amount of lactose in a mother's milk is not affected by dietary restrictions. Whether she drinks milk or eats dairy food or not, the amount of lactose in her milk will be the same.
Get the diagnosis right
Diagnostic testing for milk allergy or intolerance in young infants has limitations and may not always provide clear answers. Lactose intolerance tests can give false positive results in cases of lactose overload. Similarly, diagnostic tests for allergies are often inconclusive in babies under 12 months of age and for certain types of allergy.
In the absence of reliable diagnostic tests, assessment is based on physical signs observed by both health professionals and parents, along with a detailed description of a baby’s behaviour and feeding history. As a result, assessment depends on what is considered the most likely cause based on clinical knowledge and experience.
Improvement in physical signs and behavioural symptoms following management can help clarify the likely cause. Ideally, a stepwise elimination process is used to identify the underlying issue, so that babies and breastfeeding mothers are not exposed to unnecessary dietary restriction. However, in some cases the first-line approach is to switch a baby to a hypoallergenic infant formula.
Hypoallergenic formulas are also lactose-free and may relieve gastrointestinal symptoms associated with a range of conditions, including lactose overload. While this approach may improve symptoms, bypassing an elimination process does not provide the benefit of identifying the actual cause and may result in unnecessary cessation of breastfeeding.
It is sometimes assumed that a baby is intolerant to lactose or cow’s milk protein if symptoms resolve after switching to a soy-based infant formula. However, soy-based formulas are also lactose-free and may relieve gastrointestinal symptoms related to lactose overload rather than allergy.
Note: Maternal dietary restriction does not resolve gastrointestinal symptoms linked to lactose overload. The lactose content of breast milk is not influenced by maternal diet or dietary restriction.
GI symptoms present
Lactose overload is the most common of all problems affecting the digestive tract of newborn babies. This problem is distinguishable from the digestive disorders listed by the fact that baby is gaining weight, something that does not occur prior to milk allergy or a digestive disorder being effectively treated.
If your baby is thriving and physical signs relate primarily to her GI tract, (i.e. there are no signs such rashes, and breathing difficulties pointing to an allergy) you may find it beneficial to rule out the possibility of lactose overload before assuming her troubles are due to a milk allergy or intolerance.
GI symptoms absent
I often see babies who were diagnosed with milk allergy or intolerance despite the absence of physical signs that point to these conditions. Breastfeeding mothers are advised to restrict their diets or cease breastfeeding and babies are switched to a hypoallergenic formula in the vague hope that this might resolve distressed behavior such as persistent crying, sleep disturbance, milk regurgitation or aversive feeding behavior. A diagnosis of milk allergy or intolerance commonly occurs after medications to treat colic or acid reflux fail to resolve a baby’s troubled behavior.
In the case where there are no GI signs pointing to allergy or digestive disorder, dietary restriction or change is unlikely to improve the situation, and in fact may cause further deterioration of the status quo due to the unpleasant taste of hypoallergenic formula or as a result of ceasing breastfeeding.
When additional support may help
If symptoms persist, worsen, or diagnosis remains unclear, individualised assessment can help distinguish feeding management issues from true allergy or intolerance.
Support that considers feeding patterns, growth, and overall wellbeing may help avoid unnecessary dietary restriction or repeated formula changes. A personalised assessment with an experienced consultant to identify all possible feeding problems and provide tailored solutions.
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By Rowena Bennett
About Rowena
Rowena Bennett (RN, RM, CHN, MHN, IBCLC) is a leading infant-feeding and sleep specialist and author of several books on infant feeding and behaviour, including the widely acclaimed “Your Baby’s Bottle-Feeding Aversion: Reasons & Solutions". With over three decades of clinical experience across child health, midwifery, mental health, and lactation, she has helped thousands of families worldwide understand and resolve complex feeding challenges through her evidence-based, baby-led approaches.