Is ultrasound harmful? If so, what is it? If not, why?

Low-dose ultrasound is a potential carcinogenic and teratogenic factor, and different frequencies and sound intensities are harmful to different individuals. Because ultrasonic wave has a strong penetration ability to both solid and liquid, when the energy is large, it can make the material particles vibrate at high frequency, and part of the energy can also be converted into heat energy, which will raise the local temperature. When high-intensity pulsed ultrasound propagates in liquid containing micron-sized bubbles, it can cause bubbles to contract, expand and even explode violently. This phenomenon is called "cavitation". Not long ago, Carstensen, a famous American super biophysicist, pointed out that the maximum output intensity of some ultrasonic image diagnostic instruments currently used in clinic has reached 1kw/cm2, which is enough to make organisms generate transient cavitation. For living things, the cells near the explosion bubble will be damaged in the process of transient cavitation. Generally speaking, in most human organs and biological fluids, a small number of cells will not be harmed.