Overview of Lactose Intolerance

Symptoms, Diagnosis and Treatment

Woman shredding cheese with grater
Adam Gault/OJO Images/Getty Images

Lactose intolerance is a condition in which a person experiences digestive symptoms following the consumption of a dairy product. Lactose intolerance is caused by an insufficient amount of a digestive enzyme called "lactase." The enzyme lactase is produced in the lining of the small intestine and needs to be present in order to digest lactose, a type of sugar found in dairy products. It is the inability to digest lactose that leads to the unpleasant digestive symptoms of lactose intolerance.

What are the symptoms of lactose intolerance?

A person who suffers from lactose intolerance may experience the following symptoms shortly after eating foods that contain lactose:

Is lactose intolerance the same as a milk allergy?

No, a milk allergy, as in any type of food allergy, is a response triggered by the immune system. Lactose intolerance is a problem located within the digestive system.

Which foods contain lactose?

Lactose is found in the following dairy products and in packaged foods that contain dairy products. Make sure to read labels carefully.

  • Milk
  • Soft cheese, such as ricotta or cottage cheese
  • Ice cream
  • Yogurt
  • Butter

How is lactose intolerance diagnosed?

If you suspect that you have lactose intolerance, discuss your concerns with your doctor and ask about lactose intolerance testing. They may simply recommend that you try an elimination diet.

This would entail cutting out all dairy products, or products made with dairy products, for a period of time and then assessing this restriction effect on your symptoms.

Your doctor may also have you take a hydrogen breath test. This involves drinking a preparation containing a large amount of lactose and then administering a breath test two hours later to test for the presence of hydrogen.

If you have lactose intolerance, the lactose you drank would not be digested in the small intestine. Rather, it would pass through to the large intestine, where it would meet up with intestinal bacteria triggering the process of fermentation. This fermentation gives off hydrogen, which then would be detected by the hydrogen breath test. If you don’t have lactose intolerance, the lactose would be digested in the small intestine and there would be no rise in the level of hydrogen in your breath.

The hydrogen test has its downsides, though. For some people, the symptoms produced by ingesting the large amount of lactose can be quite uncomfortable. A small number of people do not excrete hydrogen, so the test may miss a true lactose intolerance condition. Other diagnostic options include a genetic test, blood work for glucose levels, urinary lactose testing and a small intestine biopsy. These tests are rarely performed.

If I have lactose intolerance, does this mean I can never eat dairy products again?

No, some individuals with lactose intolerance can handle small amounts of lactose without becoming symptomatic. Once you have maintained a lactose-free diet for a period of time, you could try to slowly re-introduce dairy products.

You may find that you are able to eat some yogurt, particularly Greek yogurt, some hard cheeses or even a small amount of milk without experiencing any difficulties.

You can also try a product that replaces the lactase deficiency. These pills or liquid solutions contain the enzyme lactase, therefore enabling lactose intolerant individuals to digest dairy products.

Another option is to try lactose-free or lactose-reduced milk. The use of a food diary can help ensure that you can use these products without a problem.

Could it be something else?

Yes, there are several conditions that have similar symptoms.

If you are experiencing unusual digestive symptoms, it is important that you discuss this with your physician. Other diagnostic possibilities are irritable bowel syndrome, inflammatory bowel disease, celiac disease, malabsorption syndromes or peptic ulcer. An appointment with your doctor is imperative if you have any red-flag symptoms, such as unexplained fever, rectal bleeding, anemia or weight loss.


Ehrenpreis, E. & Ehrenpreis, B. “Lactose Intolerance: Definition, Symptoms and Treatment” Digestive Health Matters 2008 17:16-18.

Krawczyk, M. et.al. “Concordance of genetic and breath tests for lactose intolerance in a tertiary referral centre.” Journal of Gastrointestinal and Liver Diseases 2008 17:135-139.

Why Does Milk Bother Me? National Digestive Diseases Information Clearinghouse.

Continue Reading