In the Hawaiian language 'Pohaku' are stones, which can be heated and used during a massage.

from the AMTA, American Massage Therapy Association:

Hot stones add temperature to Swedish massage. This demands the body respond not only to the technique, but also to the increase of blood flow encouraged by the temperatures. Applications of heated stones (or chilled) produces a series of internal responses. Working with temperatures acts as a derivative—decreasing blood and lymph in one area by increasing blood and lymph in another.

Prolonged application of heated stones to a reflex area causes dilation of the blood vessels of related organs. In other words, the use of heated stones on isolated areas pulls blood from the refl ex organs to the tissue in those regions, resulting in warm, flushed skin. Often, this result opens the door for therapists to work even deeper on trigger points or really tight muscles.

Hydration is vital when doing hot stone massage, both internally and to the your skin. Without proper hydration, burns often occur, so if your skin appears dry, applying some form of moisturizer, such as massage oil or lotion, is a must. Remember to drink plenty of water prior to a hot stone session as well as afterwards.

Clients actively participate in the session and know they not only can—but absolutely should—let them know if the stones are too hot or they’re uncomfortable.

Clients with any of the following conditions should not receive temperature based stonework:

• Diabetes
• Cancer
• Autoimmunce dysfunctions
• Epilepsy
• Neuropathy
• Heart disease
• Skin conditions
• Recent surgeries
• Pregnancy 

for more information visit the AMTA website at:

https://www.amtamassage.org/publications/massage-therapy-journal/hot-stone-massage/