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

from the AMTA, American Massage Therpapy Association:

Cold stones add temperature to Swedish massage. Applications of chilled stones 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. Chilled stones can be particularly effective for chronic and acute conditions, such as injuries and inflammation. Cold stones help remove heat from the body and allow the client to relax the affected area.

Cold stones are also capable of helping people that suffer from migraines. Reducing the overabundant blood flow to the head and brain with cold stones can normalizing the blood flow to the area. In doing so, the therapist will be reducing or removing the pounding sensation the client is experiencing in their head while helping to calm the brain.

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/

https://www.amtamassage.org/publications/massage-therapy-journal/cold-stone-therapy-for-migraine-headaches/