Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) vitiligo ?
    ### Response:
    Vitiligo is a condition that causes patchy loss of skin coloring (pigmentation). The average age of onset of vitiligo is in the mid-twenties, but it can appear at any age. It tends to progress over time, with larger areas of the skin losing pigment. Some people with vitiligo also have patches of pigment loss affecting the hair on their scalp or body.
    