A black hard lump under the tongue may be caused by mucosal hematoma, lingual inflammation and cyst of sublingual gland. 1. Mucosal hematoma: As the patient often eats some dry and hard food or too hot and too scalded food, it may lead to hematoma of the mucosa under the tongue, which may lead to the phenomenon of a black hard lump under the tongue. 2. Tongue inflammation: due to the infection caused by tongue inflammation, which causes numbness, pain and other symptoms of the tongue, some patients may have black hard lumps under the tongue. 3. Sublingual gland cysts: cysts formed by the blockage of the duct of the sublingual gland and retention of saliva, some patients may have black hard lumps accompanied by swelling and pain. When the patient has a black hard lump under the tongue, it is recommended to go to the stomatology department of the regular hospital in time for examination and standardized treatment according to the cause.