Lactose intolerance is not actually an allergy. Lactose is the sugar in milk and lactose intolerance is the inability to digest this sugar because of a lack of a digestive enzyme called lactase in the gut. The condition, whose main symptom is diarrhoea, is usually caused by gastroenteritis bacteria or viruses damaging the gut where lactase is produced. Once the gut has recovered and repaired the damage (which may take anything from a few days to a few weeks), the enzyme will be produced once more and the intolerance will disappear. While the condition lasts, it can be managed by using either a soy-based formula or a low-lactose infant formula. Sometimes children who are lactose intolerant are able to eat small amounts of dairy products like cheese and yoghurt with no ill effects.