Thanks for writing to us.
It seems you developed contact irritant reaction with kojic acid serum. So its good that you stopped using the same.
It could have occured due to sensitivity to product or may have occured due to excessive application of serum too. Usually use of hydroquinone
or glycolic acid
or azelaic acid creams reduce Post inflammatory hyperpigmentation
. Best results can be obtained with spot chemical peels
of the affected area.
Hope that helped.