Several causes. Hyperhidrosis is the condition in which a person excessively and profusely produces sweat. This can be uncomfortable emotionally and physically. Some cases of hyperhidrosis are caused by other medical conditions such as: hyperthyroidism, hypoglycemia, neurological dysfunction, substance abuse, tuberculosis, menopause, and certain tumors. See a physician to further evaluate these issues.
Maybe nothing.... ..Except that you just normally sweat a lot. If you have always sweated profusely, it's a normal condition for you. If it just started, you may need to see a physician and find out why.