Milk allergy versus lactose intolerance: Understanding the Difference

Milk allergy and lactose intolerance are different problems, even though both can cause digestive symptoms after milk. Allergy involves an immune response to milk protein. Lactose intolerance involves difficulty digesting lactose, the natural sugar in milk. Their management is different, so choosing a replacement feed by its name alone can miss the problem.

Understand what each condition affects

Milk allergy may cause skin, gut, breathing or circulation symptoms. Some reactions are rapid, while others are delayed. Lactose intolerance commonly causes digestive symptoms such as wind, bloating, abdominal discomfort and loose stools.

Lactose intolerance does not cause anaphylaxis. If your baby has breathing difficulty, tongue or throat swelling, collapse or marked floppiness, seek emergency help rather than assuming it is intolerance. Our milk allergy guide explains the assessment of suspected protein allergy.

Symptoms still need interpretation. Wind after a feed does not prove lactose intolerance, and eczema alone does not prove a food allergy.

Consider age and recent illness

Lactose intolerance is uncommon in young babies. The familiar pattern that develops in some older children and adults is not the usual explanation for a newborn’s unsettled feeding. An adult relative’s intolerance does not diagnose the baby.

Temporary difficulty digesting lactose can follow a bowel infection or another condition affecting the gut. Some premature babies also have temporary difficulty. A rare inherited absence of lactase is a different condition that requires specialist care.

Tell the clinician about recent diarrhoea, your baby’s growth, feeding and wet diapers. Persistent symptoms or poor growth need assessment of the cause, not just a different carton of milk.

Read the replacement label carefully

Ordinary lactose free cow’s milk products and many lactose free formulas still contain cow’s milk protein. They are therefore not automatically suitable for a baby with milk allergy. Conversely, removing every dairy food may be more restriction than a child with lactose intolerance needs.

Do not change an infant’s main feed or give ordinary plant drinks as a substitute without appropriate advice. If a temporary formula change is recommended, ask when it should be reviewed and how the usual feed will be reconsidered.

Breastfeeding does not automatically need to stop

Breast milk contains lactose. Removing dairy from a breastfeeding parent’s diet does not remove that lactose, because the breast makes it. Temporary lactose intolerance is not generally a reason to stop breastfeeding.

A maternal dairy exclusion advised for milk protein allergy is a separate decision. Clarify the purpose of any dietary trial so you know what improvement is being assessed and how nutrition will be protected.

Prepare for the appointment

A food and reaction diary can record symptoms, timings and feeds without deciding the diagnosis in advance. Ask which condition is suspected and whether tests are useful. Our allergy testing guide explains why allergy tests do not diagnose lactose intolerance and why results must fit the history.