Acne can leave in its wake marks in the skin that can be highly distressing. Many people who have dark skin develop brown patches where they once had acne bumps. This is called post-inflammatory hyperpigmentation and is not true acne scarring. Post-inflammatory hyperpigmentation occurs when pigment is deposited in the skin after injury. This can be any type of injury; trauma, acne, inflammatory skin diseases, infections or virtually any other factor that leads to skin inflammation. Injury leads to the deposition of melanin (the skin's pigment) in the epidermis (the top layer of the skin), the dermis (the second layer of the skin), or both.
Post-inflammatory hyperpigmentation is usually temporary, although it can be very slow to fade. If desired, it can be treated with lightening creams that contain ingredients such as hydroquinone, tretinoin or azaleic acid (among others). Chemical peels can also be used, although these should be performed with caution as they have the potential to worsen hyperpigmentation.
In contrast to post-inflammatory hyperpigmentation, acne scars are caused when deep pimples lead to alterations in the dermis (the deeper layer of the skin) when the skin heals after a pimple. If not enough collagen is produced during healing an indented scar develops. If too much collagen is produced a raised scar can form. In contrast to post-inflammatory hyperpigmentation, acne scars are permanent. Treatments for acne scars are reviewed here.
In both cases, any ongoing acne should be treated as soon as possible in order to prevent further scarring or hyperpigmentation from developing.