These blemishes also known as post inflammatory hyperpigmentation are a common problem in acne sufferers and may take a long time to resolve naturally. Prescription treatment e.g. Retinoids , adapalene gel and azelaic acid which are frequently prescribed to treat acne may help these marks disappear. Cosmeceutical products with retinol , glycolic acid and skin lighteners will assist in reestablishing a more even skin tone. Please consult with a dermatologist for assessment and prescription acne medication of required.