according to the instructions I should let it stay long and not remove it until the acne blemishes or pimples get reduced. Well I don't know really what does that mean exactly because from my experience after using this, I didn't notice any reduction in size of my pimples. I applied 4 patches and out of 4, only 1 patch was able to absorb the impurities sufficiently. I don't know what went wrong but I'm sure I followed the instructions well. Or perhaps I should try again and see how it goes? Well I still have many patches left anyway :)