What is Vitiligo, the skin disease affecting Kim Kardashian’s son?

Kim Kardashian has revealed one of her two sons is suffering from vitiligo. Even though she has not revealed which of her two sons - Saint, 8, or Psalm, 5 - has the rare skin condition, she said the disease is now under control. Kardashian explained that vitiligo can be hereditary. Vitiligo causes the skin to turn a milky-white color.