They are flat, white and can't be felt with fingers. They spread to form very large, irregularly-shaped areas without pigmentation. They are usually on both sides of the body in approximately the same place. Their size varies from 2mm or 3mm to several centimeters in diameter. They don't hurt or itch.
Disorder also causes premature graying of hair.
Once pigment has been destroyed, melanocytes can't produce more pigment. Thyroid or adrenal disease. Hyperthyroidism and hypothyroidism. Unusual physical trauma. Your own observation of symptoms.