MSM (methylsulfonylmethane or dimethylsulfone) is a sulfur-containing molecule found in various plants and some body tissues. MSM is a vital building block of joints, cartilage, skin, hair and nails. It is an efficient source of the sulfur that is used by many of the body's structural molecules. Some peer-reviewed clinical research in the U.S. has shown MSM is safe and effective in increasing joint comfort and supporting a normal range of motion.