https://community.usms.org/swimming/f/open-water-training-and-technique/25318/reverse-sunburnI still have my number from the Chesapeake Bay swim on my arm. Apparently the permanent marker acted like SPF 100 sunscreen while the rest of my body burn to a crisp. So when the marker washed off, the pale skin where the number was remained. Theen-USTelligent Community 12