Hello,
Since you have not mentioned your age,so it can be due to pityriasis alba,pityriasis versicolor or vitiligo.
Pityriasis alba is a common skin condition mostly occurring in children and usually seen as dry, fine-scaled, pale patches on the face. Pityriasis versicolor is caused by an overgrowth of a yeast fungus and are found mainly on sun exposed areas.Vitiligo is a pigmentation disorder in which melanocytes (the cells that make pigment) in the skin are destroyed. As a result, white patches appear on the skin in different parts of the body.
Exactly what it is can only be determined after examination.For that consultation of a dermatologist will be the best. Hope it helps.Take care and pls do keep me posted on how you are doing or in case you have any additional doubts.Kind regards.
External application of ketoconazole is fine assuming it it tinea versicolor, but to use internally is not advisable with out a prescription.