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There are certain creams which can cause pigmentation if you are allergic to it.In fact in certain cases even bleaching creams used to lighten color can ironically cause darkness of skin .This is called ochronosis .Its been medically proved too.In such cases its better to use only medicated creams which are relatively safe and has low fragrance content .
You can get a patch testing done with the cosmetic series in such a case.Consult a dermatologist
who has these facilities.
are multi-factorial,and its difficult to find the exact cause to it also.It can be because of low iron level,disturbed sleep, hereditary reason ,excess sun exposure ,low water intake ,chronic illness etc.There are various combination creams available containing either kojic acid
etc.Consult a dermatologist who can access your case in detail and prescribe you the right combination.