The hot stones are usually made of basalt, a type of rock that is rich in iron, so they retain heat. River rocks are normally used because they are so smooth - they have been smoothed over time by the river's current.

The stones are immersed in water and heated in an electric heating device until they are within a certain temperature range. The stones may be placed at specific points on the back, in the palms of the hand, or between the toes.

The heat warms and relaxes the muscles, which allows the therapist to apply deeper pressure, if desired.

The warmth of the hot stones improves circulation and calms the nervous system.

And massage therapists can place stones on points that are thought to be energy centers of the body to rebalance the body and mind.