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Lactose intolerance: the symptoms, getting a diagnosis, food, and treatment
For anyone who gets gas, bloating or diarrhea after milk, anyone just told they are lactose intolerant, and parents of a child who seems to have trouble with milk. The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK, part of the NIH) says lactose intolerance means having digestive symptoms after foods or drinks that contain lactose, a sugar naturally found in milk and milk products. It says about 36 percent of people in the United States have lactose malabsorption, and that most people with lactose intolerance can still have some lactose without symptoms. This page passes on, by name, what NIDDK says: the symptoms and how it differs from a milk allergy, the causes and who gets it more, how doctors diagnose it, how much lactose many people can have and where it hides, and treatment, lactase products, calcium and vitamin D. It builds the words to say to a doctor, and prints a card to keep.
Right now
- Trouble breathing, or swelling of the lips, tongue or throat, after milk or any food: call 911. It can be a severe allergic reaction, which is not lactose intolerance (ours). A severe allergic reaction.
- A baby or child with vomiting or diarrhea who seems very sick? Call the doctor now (ours). The signs of dehydration, and when it is 911.
- Blood in the stool, black stools, or weight loss you cannot explain? That is not lactose intolerance. See a doctor (ours).
More help
- Other belly troubles: An upset stomach: find the right page · Irritable bowel syndrome (IBS) · Celiac disease · Food poisoning and stomach bugs · Vomiting and diarrhea in a baby or child.
- What can be part of it: A severe allergic reaction · Osteoporosis · Breastfeeding.
- Food, care and costs: When you need food · When you need a doctor and can’t pay · My medicines list · Symptom diary · Get ready for your appointment.
- In a crisis: Help right now (988, 911). All our free tools.
An upset stomach, and not sure this is the right page? The pages on this site for throwing up, diarrhea, heartburn and constipation, on one list.
This page and its wording were written with AI (Claude) for Scarlet Beast (our AI policy). No doctor, nurse or dietitian has reviewed it. The facts were read on October 16, 2026 on NIDDK’s Lactose Intolerance pages (NIH): the overview, Definition & Facts, Symptoms & Causes, Diagnosis, Treatment and Eating, Diet, & Nutrition (last reviewed February 2018). Ours: calling 911 for trouble breathing or swelling after milk or any food; calling the doctor now for a baby or child with vomiting or diarrhea who seems very sick; not changing a baby’s formula or feeding on your own; not stopping a prescribed medicine because it has lactose; seeing a doctor for blood in the stool, black stools or weight loss; a symptom diary and changing one thing at a time; health centers, food banks, SNAP and WIC when money is tight; and the order of the steps. What we left out: brands of lactase products, doses and amounts of supplements, research studies, and clinical pages for providers. This page saves nothing and loads no trackers.