Originally Posted by
greatbasin
I heard the same thing 15 or 20 years ago. I checked it out just now and it looks to be false. According to skincancer.org, "An SPF 30 allows about 3 percent of UVB rays to hit your skin. An SPF of 50 allows about 2 percent of those rays through. That may seem like a small difference until you realize that the SPF 30 is allowing 50 percent more UV radiation onto your skin."
....
While that is correct, the difference between being outside for an hour and a half with SPF 30 instead of 50 is essentially the same as getting one minute of sun with no sunscreen. You would get more than one minute of sun by walking from your car to the grocery store in the parking lot, coming back out, and the time to load the groceries into the car.
I do not know anyone that puts on sunscreen before going to the grocery store, or walking to work from the parking lot, or getting the mail out of the mail box, or standing at the car while the tank is filled at the pump. Say nothing of waiting for a bus at a bus stop.
50 percent of a very small number is a very small number.
There is a tiny part of the population that is that sensitive to the sun but I do not recall the name of that condition. I doubt that any of them do bike tours.