Lactose intolerance or milk allergy? Telling them apart

Two different mechanisms

Lactose intolerance means the small intestine no longer makes enough lactase, the enzyme that splits milk sugar. Undigested lactose ferments in the colon, producing gas, bloating, cramps and loose stools within a few hours.

Cow's milk protein allergy is an immune reaction to the protein, not the sugar. It can cause hives, vomiting, wheezing and, rarely, anaphylaxis, sometimes within minutes.

Who gets intolerance

Most of the world's adults lose some lactase activity after childhood; it is the normal human pattern rather than a disease. Prevalence varies enormously between populations.

Living with intolerance

• Most people tolerate about 12 g of lactose at once, roughly one glass of milk, especially with a meal.
• Hard aged cheeses and plain yoghurt contain little lactose and are usually fine.
• Lactase tablets taken with the first bite help for occasional meals.
• Keep calcium up with fortified drinks, sardines, almonds and greens.

When to see a doctor

Weight loss, blood in the stool, night-time diarrhoea or symptoms starting suddenly in adulthood are not typical of lactose intolerance and need investigation for coeliac disease or inflammatory bowel disease.