Thanks for providing more information.
Well possible causes of white pigmentation on skin may include
Vitiligo- a condition in which the body produces antibodies to the melanocytes, the cells that make pigment.
This is best treated with either a mid-to strong steroid cream such as Betamethasone Diproionate, a Vitamin D3 ointment such as Vectical or a calcineurin inhibitor such as Protopic ointment.
You can try OTC cream called Melgain lotion on the white spots at night and expose to sunlight the next day in the morning for 10 minutes.
If these fail, then the Eximer Laser.
I would recommend Vitamin C 500 mg. twice a day, Iron and Folic Acid as supplements.
Tinea Versicolor-fungal infection occurs more commonly on moist areas,excessive sweating.
You can also apply Clotrimazole cream to the affected area nightly for a month.
You can try ZNP soap or zinc pyrithione soap. Apply this in the shower, lather and leave on for five minutes, then rinse off.
Post inflammatory hypopigmentation.
Having said this,the treatments depends on the underlying cause so if your symptoms'll persist then consult your dermatologist again.
I hope this helps.
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