There are many reasons why your skin would turn dark. Sun tan, overweight, pigmentation disorders like acanthosis or melasma, nutritional deficiency etc are some conditions. Unless someone examines you, we cannot know the cause. Unless we find out the cause it is difficult and pointless to treat. You can visit me at my clinic for proper examination and treatment. Chemical peels are the best way to reduce pigmentation and improve skin tone by about 2 shades