Originally Posted by
ThermionicScott
My not-dermatologist-approved method is to abstain from showering or otherwise cleaning my skin the morning of a bike ride. Your skin oils and other grime give the UV rays something else to do, like making vitamin D.
Obviously for really long and sunny rides, sunscreen is a good idea.
This works to some extent, my addendum is your skin is only making vitamin D if you have cholesterol on board. If you are cholesterol deficient you burn faster