Bacteria and other things might become trapped in dead skin cells that have accumulated on your tongue. This might result in a dark brown or black tongue. Antibiotics are one of the culprits. If you take antibiotics, your body will stop producing new white blood cells which means you'll be at risk for developing a more serious infection if one occurs in your mouth. If you have dark spots under your tongue - especially if they're also black -- you may have oral cancer. Make an appointment with your dentist right away if you notice any changes in your tongue color. You may also want to ask your dentist about how often he or she recommends checking the color of your tongue. Your tongue should be a light pink color. Sometimes people have darker tongues because they drink coffee or tea, or use tobacco products. Other times it's because people have problems with their thyroid gland or they have diabetes. If you have questions about what might cause your tongue to be dark brown or black, talk to your doctor. The doctors at Boston Children's Hospital like to say that your tongue is a window into your health. It's easy to forget how important your tongue is until something goes wrong with it. But now that you know what your tongue looks like, go ahead and check it out next time you feel up to it!