Phonophoresis
"phono" refers to sound
"phoresis" refers to one organism or compound assisting the transport of another organism or compound"
So - phonophoresis describes a process where the heating effect from ultrasonic waves increases the permeability of skin and deliver topical medication to the underlying tissue.
Research does not support the claim that 3 MHz is a sufficient frequency to increase cellular permeability; Many studies of phonophoresis are based on in vitro (lab tests, cellular level, or non-live tissue)
The amount of medication that can be pushed under the skin is also dependent on the properties of the medication itself; medications used have different levels of "phonophoretic enhancement" based on their chemical and molecular structure
Hydrocortisone and analgesics (like salicylates and lidocaine) are the most commonly used topical agents with phonophoresis. Research shows mixed findings in the amount of anti-inflammatory drug delivered using phonophoresis compared to controls. Currently, there is very low evidence of its benefits or efficacy.