I think these are skin condition vitiligo. because among other skin conditions that are responsible for white spots on skin vitiligo is the most commonest skin disease.
Normally white spots appear due the destruction of skin color producing cells called melanocytes. If these spots are increased gradually and burn white exposed to sun then this is confirm that you are suffering from skin condition vitiligo.
Second common skin condition but it is form of depigmentation in skin is Tinea Versiculor.