Hello,
Seborrheic dermatitis is a common skin condition that causes flaky,dry, white to yellowish scales to form on oily areas esp under the
nose or anywhere on face. People with
seborrheic dermatitis produce too much sebum (the natural skin oil). Later, pityrosporum yeast grows excessively in the sebum, sometime along with bacteria, making the dermatitis more persistent.
Apart from this, these white patches can be due to pityriasis versicolor or vitiligo.