Cow's milk allergy and lactose intolerance are two of the most frequently confused conditions in children. As a Consultant Paediatrician with a special interest in allergy, I see many families who have been told their child has one when they actually have the other — or who are managing their child's diet unnecessarily because of a misdiagnosis. This article explains the key differences between the two conditions.
What Is Cow's Milk Allergy?
Cow's milk allergy (CMA) is an immune-mediated reaction to proteins in cow's milk — most commonly casein and whey. It is the most common food allergy in infants, affecting approximately 2–3% of babies. There are two main types:
- IgE-mediated (immediate) allergy: Symptoms occur within minutes to two hours of consuming cow's milk. These include hives, swelling, vomiting, runny nose, wheeze and — in severe cases — anaphylaxis.
- Non-IgE-mediated (delayed) allergy: Symptoms occur hours to days after consuming cow's milk. These include eczema, reflux, colic, loose stools, blood in stools and poor weight gain. This type is more common in infants.
What Is Lactose Intolerance?
Lactose intolerance is a digestive condition — not an immune reaction. It occurs when the body does not produce enough lactase, the enzyme needed to break down lactose (the sugar found in milk). Undigested lactose passes into the large intestine where it is fermented by bacteria, causing symptoms such as:
- Bloating and wind
- Abdominal cramps and pain
- Diarrhoea
- Nausea
Lactose intolerance does not cause skin symptoms (hives, eczema), respiratory symptoms (wheeze, runny nose) or anaphylaxis. It is rare in young children — primary lactose intolerance typically develops in older children and adults. Secondary lactose intolerance can occur temporarily after a gut infection (gastroenteritis).
Key Differences at a Glance
| Feature | Cow's Milk Allergy | Lactose Intolerance |
|---|---|---|
| Cause | Immune reaction to milk protein | Enzyme deficiency (lactase) |
| Age of onset | Usually in infancy | Older children and adults (primary); any age (secondary) |
| Skin symptoms | Yes (hives, eczema) | No |
| Respiratory symptoms | Yes (wheeze, runny nose) | No |
| Anaphylaxis risk | Yes (IgE-mediated) | No |
| Gut symptoms | Yes | Yes |
| Small amounts trigger symptoms | Yes (in IgE-mediated) | Often tolerate small amounts |
Why Does the Distinction Matter?
Getting the diagnosis right matters because the management of the two conditions is different. Children with cow's milk allergy need to avoid all cow's milk protein (and in some cases other mammalian milks). Children with lactose intolerance may be able to tolerate small amounts of lactose and can often consume hard cheeses and yoghurt, which contain less lactose than fresh milk.
Unnecessary dietary restriction in infants and young children can affect growth and nutritional status. Equally, failing to diagnose cow's milk allergy can leave a child at risk of ongoing symptoms and — in the case of IgE-mediated allergy — anaphylaxis.
Getting the Right Diagnosis
If you are unsure whether your child has cow's milk allergy or lactose intolerance, specialist assessment is the best way to get a clear answer. I will take a detailed history and recommend appropriate testing to establish the correct diagnosis and management plan.
See also: Cow's Milk Allergy in Babies and Children
Dr Mugilan Anandarajan, Consultant Paediatrician (FRCPCH, MD). Also see: belfastallergyclinic.com | belfastchildrensclinic.com