What Could Cause Black Layer Formed In Both Cheeks?

Dear sir , Im sadique , there is some black layer formed in my both cheeks before one year, still it was there in my face , its not reducing.. That black area in my face gets more darken when i go through sun light , usually im white in colour but my both cheeks looks black.. Skin in that black area alone looks different from other parts of face.. It sometimes getting reduced and sometimes it become darken.. Im suffering from this problem for past one year.. Please suggest me any medicine or treatment or any valuable suggestions.. Thank you