Though troubling in appearance, a black, hairy tongue is typically nothing serious. The small bumps on the surface of your tongue, called papillae, grow throughout your lifetime. In some people, the papillae become excessively long, rather than being worn down by daily activities. That makes them more likely to harbor bacteria. When these bacteria grow, they may look dark or black and the overgrown papillae appear hair-like. This condition is not common and is most likely to occur in people who do not practice good dental hygiene. People who are on antibiotics or receiving chemotherapy and people with diabetes may be more likely to have a black hairy tongue.