If heavy sweating has no underlying medical cause, it's called primary hyperhidrosis. This type occurs when the nerves responsible for triggering your sweat glands become overactive and call for more perspiration even when it's not needed. Primary hyperhidrosis may be at least partially hereditary.
If the sweating can be attributed to an underlying medical condition, it's called secondary hyperhidrosis.
Causes shown here are commonly associated with this symptom. Work with your doctor or other health care professional for an accurate diagnosis.