Thanks for writing in.
Darkening of skin is caused by sunexposure and hormonal
Toothpaste use of some types can give rise to perioral pigmentation like your.
Avoid any cosmetic creams or home remedies
Chemical peeling can give you fast and long lasting results.They are available at dermatology clinics.
Apply cosglo cream at night.Take vitamin C
You can use gel based sunscreen like Zoray acquagel sunscreen.
Hope this helps.