Cow's milk allergy (CMA) and lactose intolerance are not the same but they are often confused with each other because they are caused by the same thing (milk) and they share some of the same signs and symptoms. These include feeding and bowel problems such as wind, diarrhoea, bloated tummy, tummy aches and cramps, tummy rumbling and feeling sick. However, since CMA involves the immune system, babies who are allergic to cow's milk protein may also show allergy symptoms like an itchy rash, wheezing, or runny noses and coughs. These aren't seen in lactose intolerance, as this condition doesn't involve the immune system.

With lactose intolerance, the digestive system can't fully digest lactose, which is the sugar found in milk. So instead of being digested and absorbed, the lactose stays in the gut and causes the symptoms of lactose intolerance. For example, the lactose may be metabolised by bacteria to produce acids and gases that lead to discomfort. Lactose intolerance may occur temporarily, e.g. following bouts of tummy bugs, and in these cases will usually resolve in the short term. Other cases of lactose intolerance may be lifelong, such as in those born with a primary lactose intolerance or those who develop it as they get older. Lactose intolerance caused by inheriting a genetic fault (known as primary lactase deficiency) is uncommon before 2–3 years of age.

Another difference is that with CMA, even a small amount of cow's milk protein could give your baby an allergic reaction. In contrast, babies with lactose intolerance can often tolerate small amounts of lactose and can tolerate cow's milk protein fully.

Cow’s milk allergy	Lactose intolerance
An allergic reaction to proteins in cow’s milk	The inability to digest the milk sugar lactose
Involves the immune system	Doesn’t involve the immune system
Gastrointestinal, skin and respiratory symptoms may be involved	Symptoms are only gastrointestinal, such as diarrhoea. No skin and respiratory symptoms are involved
A small amount of cow’s milk protein could cause an allergic reaction	A small amount of lactose can often be tolerated. Cow’s milk protein doesn’t cause any allergic reactions

If you are still confused about the difference between cow’s milk allergy and lactose intolerance, speak to a healthcare professional.

CMA or lactose intolerance