[13ren]

Intriguingly, bike shops do not sell long sleeve tops (that protect you from sunburn) - but surf shops do. Cyclists have told me that they don't get sunburn - even when cycling in the sun all day. But surfers do get sunburn. I'm not sure what to make of this.

I'm theorizing that cyclists are somehow protected by constant movement (unlike surfers waiting for a wave). Perhaps the airflow is protective? Or perhaps it makes cyclists aerobically fitter, and this makes their skin more resistant to sunburn (and therefore skin cancer).

[zenlinux]

I'm an avid cyclist and I can sunburn easily if I don't use sunblock. I would say that surfers are more likely to burn (and do so more quickly) simply because beaches don't have much shade. While riding a bicycle you can often duck into tree shadows during a ride.

Some cyclists do use long-sleeve summer jerseys, but they're in the minority. Short sleeve and sleeveless jerseys are more popular because they are cooler.

[Shooter]

The explanation is much simpler: You burn much faster on or in the water because of the reflections from the water...you're basically sitting on a giant mirror.

I fried myself once when I was sailing, and I had the worst burns on the bottom parts of my body (bottom of chin, bottom of knees, basically anywhere the rays hit me after bouncing off the water.)