What is a clear bump on the underside of your tongue?

A clear bump on the underside of your tongue could be a mucocele. A mucocele is a small, fluid-filled sac that can develop on the inside of the lip or on the underside of the tongue. Mucoceles are caused by a blocked salivary gland duct. When the duct is blocked, saliva can build up and cause a swelling. Mucoceles are usually not painful, but they can be unsightly. Treatment for a mucocele typically involves draining the fluid from the sac.