Vitiligo is a permanent skin condition that causes white patches to form due to the lack of a chemical called melanin. It's not exactly clear what causes this lack of melanin, but there's one thing we do know - vitiligo is beautiful.
Thousands of people have taken to social media today, the official World Vitiligo Day, to showcase their skin and what makes them unique.
Canadian supermodel Winnie Harlow features prominently in the posts, having made headlines with her incredible story of beating the bullies to become a world-famous catwalk star.
"Growing up for me was extremely tough in a social sense, I was teased and ridiculed because of my skin," she wrote in a blog post on fabfem.co.uk.
Harlow proved that having vitiligo is no barrier to success in the fashion business, claiming that when she learned to love herself, "opportunities started to fall into my lap and I thank God for all of them."
Here's what some inspirational Instagram users had to say with the hashtag #WorldVitiligoDay: