Dark skin after waxing in chin, what to do? (photo)

What you are experiencing most likely is called Post Inflammatory Hyperpigmentation. It may have been due to the warmth of the waxing or the trauma from pulling at the hairs. Sometimes just the irritation of the waxing causes discoloration. It will fade. There are topical creams containing hydroquinone that can lighten the skin, but time will also see improvement.
In the future, laser hair removal is a good alternative.
Good luck, take care.

The hyper pigmentation from waxing can be treated with a combination of hydroquinones and mild cortisone.  If there is any hair that is there I would treat it first so that this condition is treated first.  Depending on your skin type the Gentle Yag may be the best laser for you.  Please find a board certified dermatologist with a great deal of experience in laser hair for the best results.