It depends on the skill and professional knowledge of the operator, that is, the beautician. If you have a good understanding of facial channels and collaterals and use them properly, it will have certain effects. But as far as I know, there are very few beauty practitioners who have reached this level at present, so you must be careful to identify them, especially if there are so-called black substances, which must be deceptive. How do human pores excrete black substances visible to the naked eye?