The symptoms of lactose intolerance occur when lactose that hasn't been broken down by lactase is instead broken down by bacteria. They can vary based on how much dairy you consume, how little lactase your body produces and how your own body responds.
Symptoms begin anywhere from about 30 minutes to two hours after dairy consumption.
That's nice, but what are the symptoms?
Possible symptoms include bloating, gas, diarrhea, stomach cramps and nausea.
None of these are very fun, but there are ways to alleviate (below) or eliminate the symptoms. Note that these symptoms usually get more apparent with age.
Be sure to check with a doctor
These symptoms can apply to other conditions or even other diseases, so it is important to go to a doctor if you think you have lactose intolerance.
There are a few ways to test for lactose intolerance. One way is the hydrogen breath test, where you will be given a drink containing lactose and then monitored for the level of hydrogen in your breath (hydrogen forms in the stomach as undigested lactose ferments in the colon).
Other ways are an enteroscopy, where an instrument is used to look around your intestines inside your body; or a milk test, where you avoid all dairy for three or four days and then see how your body reacts when it is reintroduced to your system. The milk test is generally not recommended without the guidance of a dietician.
How to alleviate symptoms
Even if you are careful about what you eat, chances are that you will occasionally make a mistake (like forgetting your lactose supplement or eating a bit too much dairy). When that happens, you can't avoid the symptoms, but you can try a couple tricks to make yourself feel better. Eat something without dairy to dilute the amount of dairy your stomach has to deal with. Drink a lot of water to help move things along. Take Pepto Bismol or something similar for nausea, upset stomach or diarrhea. If you experience a lot of bloating or gas, a gas-relieving agent such as Gas-X can help.