kindly send pictures of affected area for accurate diagnosis.

Greetings. The black mark may be due to many reasons. Without a detailed history or examining it or without seeing tis photo - i cannot comment on the diagnosis or the treatment. Kindly reply with photos or see a qualified dermatologist near you. Warm regards

?periobital melanosis. Depending up on the cause for it we need to treat. There may be several causes like nutritional (decreased Hb%, ,vitb12 level, ferritin level), stress, post pregnancy, lack of sleep, Refractive error of eyes, type of work, reading book in less light, latop & mobile excessive users, on the top of if its running in hereditary its very resistant for the treatment. Chemical peels,lasers, topical application ...correction of the above said causes can be useful. Cearms like wunder eyes/ iglow under eye gel/ Roc sublime correction creams..etc, may be useful .  Vitamin &antioxidant creams also helps in some extent.