What Causes Pigmentation On The Face With Black Scars On The Nails?

Dr, i had many black nail scars bought about by my brother in childhood which has not faded .
I have fair complexion on my rest of the body excluding face which is slightly darker (.i didnt took care of my skin till recently , had many sun exposures, many nail scars, dark circle)So i consulted a skin speacialist on july 2010 and he prescribed skin lightning cream-melalite 15 cream(Hydroquinone USP 2% w/w, Oxybenzone USP 2.5% W/w, Octinoxate USP 9.0% w/w) which contain hydroquinone . i got best results after application within 1and half months..and discontinued till today..now it seems tat the previous results are unchanged(i think it can be due to body changes)..and i wish to start its application.
BUT I FOUND ON internet tat hydroquinone is dangerous sometimes get opposite results,carcinogenic,long term use can cause darker complexion....and in my case i want to apply just for 2-3 months...my doubt is this term is long term and is am risking?
would it cause dependency (i mean, stopping using it after the prescribed period would go back to the condition before treatment??) ?
Am sticking on tat cream coz i found it had better results on my skin and i didnt had any allergic reaction or itching,etc..also i dont want to waste time and energy on trying other products..
And a big thanks dr