Why Are These Runners Racing In Their Underwear?

These runners are stripping down for a good cause.

Every February, runners strip down to the bare necessities for the annual Cupid’s Undie Run. In 39 cities across the world, these runners spend their Valentine’s Day raising funds for the Children’s Tumor Foundation. Fundraisers have the chance to earn swag for their efforts, all leading up to the “brief” one-mile fun run.

Check out these photos from the race series to see what the no-pants party is all about.