Differin has a rather lengthy exacerbation period. I believe at least 12 weeks during which your acne will probably worsen before it begins to show improvement. While this can be unsettling, I found that it was worth the (four) months it took to begin to have a positive effect on my acne. Also, after I complained to my doctor, he prescribed me an oral antibiotic (doxycycline) to accompany the Differin gel. Together, they still keep my skin perfectly clear (it's been almost four years).