Allergy
Milk Allergy vs Lactose Intolerance: What is the Difference?
A simple guide for parents on the difference between cow's milk protein allergy and lactose intolerance in babies and children.
Patient information page | Last reviewed: June 2026
The quick answer
Milk allergy and lactose intolerance are not the same. Milk allergy is an immune reaction to cow's milk protein. Lactose intolerance is a digestive problem caused by difficulty breaking down lactose, the natural sugar in milk. The treatment is different, so it is important not to guess.
- Core difference
- Compare symptoms
- Babies and lactose intolerance
- Treatment differences
- Safety reminders
When a baby or child is struggling with feeds, reflux, tummy symptoms, rashes, or unsettled crying, the medical terms can become confusing. People sometimes use “milk allergy” and “lactose intolerance” as if they mean the same thing, but they are different conditions.
Understanding the difference helps your doctor choose the right plan and helps avoid unnecessary food restrictions.
1. The core difference
Cow's milk protein allergy
This is an immune system reaction. The body reacts to proteins in cow's milk as if they are harmful. It may cause immediate symptoms or delayed symptoms.
Lactose intolerance
This is a digestive problem. The body has difficulty breaking down lactose because there is not enough lactase enzyme. It does not involve the immune system.
2. Comparing the symptoms
| Feature | Milk allergy | Lactose intolerance |
|---|---|---|
| What is the problem? | The immune system reacts to milk protein. | The digestive system cannot break down milk sugar properly. |
| When does it usually start? | Often starts in infancy or early childhood. | Primary lactose intolerance is uncommon in babies and is more common in older children, teenagers, and adults. |
| Common signs | Hives, swelling, vomiting, reflux, blood or mucus in stool, eczema, diarrhoea, wheeze, or poor growth depending on the type. | Bloating, gas, tummy pain, watery diarrhoea, and discomfort after lactose-containing foods or drinks. |
| Can it affect breathing? | Yes. Severe immediate allergy can cause wheeze, throat symptoms, breathing difficulty, or collapse. | No. Lactose intolerance does not cause breathing symptoms. |
| Can it affect the skin? | Yes. It can cause hives, swelling, or eczema flares in some children. | No. Lactose intolerance does not cause hives, swelling, or eczema. |
3. A note on babies and lactose intolerance
True long-lasting lactose intolerance is rare in infants. Babies are usually able to digest lactose because milk is their main food source.
Some babies and children can develop temporary lactose intolerance after a stomach infection or gut irritation. This is sometimes called secondary lactose intolerance. It usually improves as the gut lining heals.
4. How the treatments differ
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Milk allergy: cow's milk protein needs to be removed from the diet. If a baby is formula-fed, a doctor may recommend a hypoallergenic formula such as extensively hydrolysed formula or amino acid formula.
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Lactose intolerance: the issue is lactose, not milk protein. A doctor or dietitian may suggest a lactose-free option for a limited period or longer term, depending on the child’s age and cause.
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Lactose-free milk is not a treatment for milk allergy: lactose-free cow's milk still contains cow's milk protein, so it can still trigger symptoms in a child with cow's milk protein allergy.
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Do not switch infant feeds without advice: babies need specific nutrients for safe growth, so special formulas and restrictive diets should be used with medical guidance.
5. Safety reminders
Keep a symptom diary
Record feeds, foods, vomiting, stools, crying, skin symptoms, breathing symptoms, medicines, and timing. This helps your doctor see the pattern.
Avoid unnecessary restriction
Do not remove major foods from a baby or child's diet without advice. This can affect nutrition and growth.
Related guide
If cow's milk protein allergy has been suspected or diagnosed, see also: Understanding Cow's Milk Protein Allergy in Infants.
When to get urgent help
Call emergency services immediately if your child develops swelling of the lips, tongue, or throat, difficulty breathing, wheezing, a hoarse voice, floppiness, extreme drowsiness, collapse, or rapidly worsening symptoms after having milk.