Ever wondered why a glass of milk sometimes leaves your stomach feeling uncomfortable? Lactose intolerance may be the reason. It happens when the body does not produce enough lactase, an enzyme needed to digest lactose, the natural sugar in milk.

People with lactose intolerance may experience bloating, stomach cramps, gas, or diarrhea after consuming dairy products. Symptoms can appear after drinking milk, eating ice cream, or having foods made with regular milk.

So, where does lactose come from? It is naturally present in cow’s milk, goat’s milk, and other animal milks, as well as products made from them, including cheese, yogurt, cream, and some desserts. However, not every dairy product affects people in the same way. Some cheeses and yogurts contain less lactose and may be easier to tolerate.

Teens who notice repeated discomfort after consuming dairy should talk to a doctor or registered dietitian rather than simply avoiding all dairy. Lactose-free milk and dairy alternatives can also provide options.