Cow's milk allergy vs lactose intolerance: a guide

A baby who is unsettled after feeds, has loose poos or a flare of eczema is often labelled "lactose intolerant" by well-meaning relatives. Sometimes the real issue is cow's milk allergy. Sometimes it is neither.

The two conditions sound similar and can cause overlapping tummy symptoms, but they involve different parts of the body and carry different risks. Getting the distinction right matters, because the wrong formula or an unnecessary elimination diet can affect a baby's growth and nutrition.

This guide explains the difference, the symptoms to look for, how diagnosis works in Australia and what to do if you are worried. It is general information, not a diagnosis.

The one-line difference#

Cow's milk allergy (CMPA) is an immune reaction to proteins in cow's milk. It can cause immediate allergic symptoms, including anaphylaxis, or delayed symptoms such as eczema and gastrointestinal problems.

Lactose intolerance is a digestive problem. The body does not make enough lactase, the enzyme that breaks down lactose, the sugar in milk. It causes wind, bloating, pain and diarrhoea. It is uncomfortable but not dangerous, and it does not cause hives, swelling or anaphylaxis.

What cow's milk allergy can look like#

ASCIA describes two main patterns.

Immediate, IgE-mediated reactions usually happen within 15 minutes and up to two hours after drinking cow's milk or eating dairy. Symptoms can include:

• hives or welts
• swelling of the lips, face or eyes
• vomiting or abdominal pain
• diarrhoea
• noisy breathing or wheeze
• swelling or tightness in the throat
• pale, floppy or unusually sleepy behaviour in a young child

Anaphylaxis is a medical emergency. It requires immediate adrenaline and a call to 000.

Delayed, non-IgE-mediated reactions usually happen two or more hours later. They can include an increase in eczema, delayed vomiting, diarrhoea or blood in the poo. Allergy tests are often negative for these reactions, which is why the history matters.

CMPA is more common in babies with a family history of allergy, but it can happen in any family. It is not caused by something the mother did or did not do during pregnancy.

What lactose intolerance looks like#

Lactose intolerance causes symptoms when lactose reaches the large intestine and gut bacteria break it down. The result is gas, bloating, cramps and diarrhoea. Some children also feel nauseated.

In babies, true lactose intolerance is very rare. It can happen temporarily after gastroenteritis, when the gut lining is inflamed and produces less lactase. Some babies with significant gut inflammation or short bowel conditions may also have it, but that is a medical diagnosis.

Lactose intolerance does not cause eczema, hives, lip swelling or anaphylaxis. If those symptoms are present, allergy is the more likely explanation and needs urgent assessment.

Why the difference matters#

The treatment is not interchangeable.

For CMPA, the trigger is milk protein. That means:

• most lactose-free formula is not suitable, because it is still made from cow's milk protein
• goat's milk, sheep's milk, camel's milk and A2 milk are not suitable
• partially hydrolysed (HA) formula is not suitable for treatment
• extensively hydrolysed formula (EHF) is usually the first choice
• an amino acid-based formula (AAF) is needed for around one in ten babies with CMPA
• soy formula is usually only considered for babies over six months and is not suitable for every child
• rice protein formula may be an option under specialist advice

For lactose intolerance, the trigger is lactose. A low-lactose diet for a short period may be suggested, followed by a supervised reintroduction. Most children can tolerate small amounts of lactose, and hard cheese and yoghurt are often better tolerated than milk.

Removing dairy entirely without a plan can lead to inadequate calcium, protein and energy intake. That is especially risky for a growing baby or toddler.

How diagnosis actually works#

A diagnosis should start with a detailed history: what was eaten, how much, how soon symptoms started, what they looked like and how long they lasted. Photos and a food diary can help.

For immediate reactions, skin prick tests or specific IgE blood tests can support the history. For delayed reactions, these tests are often negative, so a supervised elimination trial is more useful.

ASCIA describes a typical trial as removing cow's milk and other dairy foods for one to four weeks, then planning a reintroduction to confirm the diagnosis. That reintroduction should be supervised, especially if the reaction was severe. Do not keep a child on a long-term elimination diet without follow-up.

Tests such as IgG food testing, hair analysis, kinesiology, vega testing and cytotoxic testing are not valid ways to diagnose food allergy. If a practitioner offers one of these, ask for evidence and consider a second opinion.

If you are breastfeeding#

A breastfed baby can react to cow's milk protein from the mother's diet. However, excluding dairy from the mother's diet is rarely required, and it should only be done with advice from a doctor or dietitian.

If you do exclude dairy, you need a plan for calcium, protein and energy. Read labels carefully, because milk solids, whey, casein and milk powder appear in many foods. A dietitian can help you avoid accidental exposure without making the diet unnecessarily narrow.

Lactose is still present in breastmilk even when a mother avoids dairy. That is why a dairy-free maternal diet does not treat lactose intolerance in a breastfed baby.

Starting solids and the milk ladder#

If your child has CMPA, speak to their allergy team before introducing baked or cooked milk. Some children tolerate baked milk in muffins or cakes, but this should not be trialled at home unless you have been advised it is safe.

Read food labels every time, because recipes change. Milk can appear in bread, biscuits, chocolate, sauces, processed meats, stock cubes and "dairy-free" products that are made on shared equipment. Also check dental products: ASCIA warns that some toothpastes and chewing gums contain Recaldent, which is derived from cow's milk protein.

For general allergen introduction, see our food allergy guide and starting solids guide. If your baby is diagnosed with CMPA, a dietitian should review their nutrition, especially if they are avoiding multiple foods.

When to get help#

See your GP or child and family health nurse if your child has:

• blood or mucus in their poo
• persistent diarrhoea, vomiting or tummy pain
• poor weight gain or feeding difficulties
• eczema that is not improving with usual care
• a suspected reaction to milk or dairy

Ask for an urgent review or call 000 if there is any breathing difficulty, throat swelling, collapse or a rapidly spreading rash with vomiting.

The bottom line#

Cow's milk allergy and lactose intolerance are not the same, and the treatments are different. CMPA is an immune reaction to milk protein and can be serious; lactose intolerance is a digestive reaction to milk sugar and is uncomfortable but not dangerous.

If you suspect either, keep a record of symptoms and get a proper assessment. Do not switch to lactose-free, goat's milk or A2 formula for a suspected allergy, and do not remove dairy from your child's diet long-term without dietitian support. The right diagnosis makes feeding safer and simpler.