What causes blistering of the skin during an UltraShape treatment?

Typically there is no blistering, but you could have had a reaction to taping or strapping which is commonly used with Ultrashape. Otherwise, the device can create some thermal effects. If you have some blistering it will likely resolve. I would alert my provider. 

Thanks for your question. This is typically an uncommon occurrence. This treatment works by using ultrasound waves that penetrate about 1.5cm deep into the subcutaneous fat. The sound waves damage the fat cells leading to permanent destruction. Occasionally, some of the sound waves will not penetrate as deeply and the sound waves will try to exert their effect on more superficial structures like the skin. This may lead to transient blisters or small broken blood vessels, all of which resolves very quickly without scar formation.