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If it is involving both the angles of mouth ,then it must be ANGULAR CHEILITIS
or ANGULAR STOMATITIS
It can be because of any of the following reasons:
or bacterial infection (can be secondary also)
vitamin B deficiency
Treatment would begin with oral anti fungal and anti bacterial agents.Along with this one should take a long course of oral vitamin B complex medicines.
So keep your general condition good and you would see a early response.