Milk intolerance
Lactose intolerance is a common digestive problem where the body is unable to digest lactose, a type of sugar mainly found in milk and dairy products.
Lactose intolerance is usually caused by your body not producing enough lactase - an enzyme (protein that causes a chemical reaction to occur) that digests lactose.
It's important to visit your GP if you think you or your child may have lactose intolerance, as the symptoms can be similar to other conditions.
There's no cure for lactose intolerance, but most people are able to control their symptoms by making changes to their diet.
Zoe Bastion is an assistant content producer at the BBC. She has had primary lactose intolerance for most of her life.
Gary Alexander is a writer and author who lives in London. He suffered from secondary lactose intolerance for several months after a severe bout of gastroenteritis.