On the other hand, around 15-20% of people have some degree of lactose intolerance, which has nothing whatsoever to do with allergy or the immune system. This is simply a shortage in the bowels of the enzyme Lactase, which is required to digest the sugar lactose, which is found in milk. People are born with this shortage and some have it worse than other's.... i.e. one person might have zero Lactase, none at all, and get sick with any dairy intake whatsoever. Another person might have 50% of the "normal" amount of Lactase, and they can tolerate dairy in small quantities but not in large amounts. What's more, a person's supply of Lactase can fluctuate... in particular, Lactase can get "knocked out" by certain stomach bugs and take weeks to regenerate, making someone who is usually Lactose tolerant temporarily lactose intolerant, or making someone who usually has a mild lactose intolerance temporarily more severe.

The reason people with Lactose intolerance get sick it that it's not normal to have undigested sugars passing into the lower intestine. When they do two things happen... water is drawn into the bowels from the blood stream to dilute the sugar but making the stools looser, and the normal bacteria that colonize the bowels have a feast on all this extra food and cause a lot of gas and cramping.

The best treatment for Lactose Intolerance is Lactaid or Dairy Ease - products which can be added to food to replace the missing lactase. These are very safe for all ages and are readily available without a prescription. Avoidance of dairy products also works, but is generally unnecessary. Lactaid come pre-mixed in "Lactaid Milk", and also is available as drops and pill for use with other diary products such as cheese which one might ingest. The dose does not depend on size of the child, but rather the amount of dairy to be consumed.

While Lactose Intolerance can be confirmed by a test called a Lactose Breath Hydrogen Test (LBHT), this is not usually necessary. The diagnosis can usually be suspected based on history, and confirmed by a trial of Lactaid or Dairy Ease - sometimes after a trial of eliminating milk from the diet narrows down the possibilities to Lactose Intolerance or Milk Allergy (which is not helped by these medications).