Is ThermiSmooth ok for tightening under eye hollowness or is it hype?

ThermiSmooth helps the body produce more collagen in the dermis of the skin. This collagen helps tighten loose skin to some extent but does not build up volume of underneath tissues to fill in hollowness. Fillers are used to revolumize the face.The information provided in Dr. Shelton's
answer is for educational purposes only and is not intended
to constitute medical advice. The information provided should
not be relied upon as a substitute for consultations with a qualified
health professional who may be familiar with your individual medical
needs.

ThermiSmooth will help tighten the loose skin under the eyes. Hollowness is caused by volume loss. If you have loose skin under your eyes it will help. If your main issue is hollowness from volume loss then fillers may be more appropriate. Hope this helps.