Thanks for using Health Care Magic,
This may be due to a skin infection
,allergy or autoimmune disorder.
If it is a fungal infection
like tinea versicolor
there might be itching and scaling of the skin.This can be treated by antifungals.It can be due to vitamin deficiency
and can be treated by b complex tablets.
Sometimes rarely it might turn out to be vitiligo,or any precancerous skin lesion.It is advisable to consult a skin specialist and undergo skin tests for further treatment.