My Dear Welcome to Healthcaremagic! I have analyzed your problem and feel that it is not necessarily vitiligo although it is not possible to rule it out at the moment. this might have resulted from sun exposure, especially s you are using just an 15SPF preparation which is too less than the desired level of 30-35. Moreover, your method of application may not have been explained to you by your prescribing doctor. The condition that closely mimics your description is Polymorphous Light eruption. here goes the sunscreen use instructions 1 apply daily at 1030 Am and repeat at 100PM 2 Use even indoors or on cloudy days 3 use at last 30 minutes before intended sun exposure 4 SPF of 30 at least 5 Physical avoidance of sunlight is better than using sunscreens 6 wear hats or long sleeves to protect additionally. You might like to change your usual manner of sunscreen use now with great benefit. We wish to see you well soon.