Causes of diarrhoea in infants

A sudden change in loose or watery stools may occur with gastroenteritis or food poisoning. Giardiasis is another infection that can disturb digestion. Some babies react to a component of food or formula; food intolerance can cause loose stools, wind or discomfort. Persistent symptoms need assessment for conditions such as coeliac disease, Crohn's disease or, less commonly, an overactive thyroid.

Breastfed babies normally have softer stools than older children, so the change from your baby's usual pattern matters. Note stool frequency, colour, blood or mucus, vomiting, fever, feeding and wet nappies.

Continue breastfeeds or usual formula unless a clinician advises otherwise. Offer feeds more often if your baby is willing, and do not dilute formula. Avoid giving anti-diarrhoea medicines or changing formula without medical advice. Keep a record of feeds, wet nappies and stools so a clinician can judge hydration and the pattern.

Contact a clinician promptly if your infant has fewer wet nappies, a dry mouth, no tears, unusual sleepiness, repeated vomiting, blood in the stool, a swollen abdomen, fever, or is feeding poorly. Seek urgent help if your baby is difficult to wake, has trouble breathing, or you are worried about dehydration. Young infants can become unwell quickly.

Ask whether the stool pattern suggests infection, intolerance or another cause; how to maintain feeds; which signs show dehydration; and whether your baby needs an examination or stool testing.