Symptoms of lactose intolerance can be mild or severe, depending on how much lactase your body makes. Symptoms usually begin 30 minutes to 2 hours after eating or drinking milk or milk products. If you have lactose intolerance, your symptoms may include:

• Bloating.
• Pain or cramps in the lower belly.
• Gurgling or rumbling sounds in the lower belly.
• Gas.
• Loose stools or diarrhea. Sometimes the stools are foamy.
• Throwing up.

Many people think they are lactose-intolerant because the symptoms of lactose intolerance are very common symptoms. If you feel sick after drinking a glass of milk one time, you probably do not have lactose intolerance. But if you feel sick every time you have milk, ice cream, or another dairy product, you may have lactose intolerance.

Sometimes people who have never had problems with milk or dairy products suddenly have lactose intolerance. This is more common as you get older.

Symptoms of the most common type of lactose intolerance-adult lactose intolerance-often develop during the teen or adult years and continue for life. Symptoms of acquired lactose intolerance last as long as the small intestine does not make lactase.

In rare cases, newborns are lactose-intolerant. Symptoms in newborns include severe foamy diarrhea, diaper rash, vomiting, dehydration, weakness and irritability, and slow weight gain.

If you think you might have lactose intolerance, talk it over with your doctor. Your doctor can make sure that your symptoms are caused by lactose intolerance and not by another problem. Other conditions can cause symptoms similar to those of lactose intolerance, including irritable bowel syndrome, inflammatory bowel disease, overuse of laxatives, and problems digesting foods that contain fructose and sorbitol.