Do you always wear sunscreen on sunny days when your out on your bike? I read an article in Readers Digest saying that you should be out in the sun everyday for 15 to 20 minutes without sunscreen to get your vitamin D. It says that vitamin D can actually help reduce the risk of some cancer's as well as other health problems and you can't overdose on vitamin D from the sun, but the threat of sunburn continues. It said for best results, expose at least 50 percent of your body, wearing shorts and a T-shirt or a bathing suit, if possible.

Actually I don't like to wear sunscreen when riding at all, even when I lived in the Mojave Desert area of California and rode into the mountains! Why? Am I insane? Perhaps, but I found that sunscreen made me hotter! HOWEVER, if your have a very light complexion wear sunscreen, the protection is worth the extra heat. I have a darker complexion so the sun never damaged my skin. But I do wear sunscreen when I'm going to be near or on water. When I lived along the coast of S Cal I wore sunscreen because first off it was cooler there, and second the coastal haze allows the sun to fry your skin fast, and third I would find myself riding along the beach at some point during the ride; so the added effect of the haze and light reflecting off the water would compound the suns effect on your skin.

By the way the Readers Digest report is accurate but I think it also says that too much of a good thing can be bad, that's why they only talk about 15-20 minutes, anything over that you could be at risk for skin cancer. When I rode my bike in Calif I rode with shorts and a short sleeve jersey on so only my legs, arms, and face got exposed. Keep in mind when your riding a bike your constantly turning in different directions exposing different areas of your body all the time, so the sun never sets on you in one spot like it would if you were lying on a beach. And the helmet and glasses offer some shade relief as well. And when your back is to the sun you get very little sun on skin surfaces when riding.

I believe that getting adequate sun exposure is more of a problem in winter when daylight hours are short. Fortunately, the need for sunscreen in most areas is reduced in winter.

Don't use sunscreen at all but with sun at my back I get a problem with the back of my neck. Easy cure is to wear a bandana at the back of the helmet to cover the neck.

I don't burn on my arms or legs, but I burn fast on the back of my neck, nose, just above my eyebrows, and the area directly below my eyes. I always put on sunscreen if it is going to be sunny out, though after a while it pretty much becomes useless with the amount I'm sweating.

Pfffft, you believe stuff that is in the readers digest? That article is a bit of bull IMHO.
Talking to a doctor and they said all you need is 5 minutes a day on the area of skin the size of the back of your hand.

The real concern with this issue is that some people, such as those in nursing homes don't get to go outside at all.

If you are still concerned, at least put sunscreen on your face and neck, the parts that get sun pretty much any time you are outside. If you at other figures it only takes 15 to 20 mins a day on unprotected skin to get skin cancer. Coming from the melanoma capital of the world, it's something I'm a bit opinionated about.

As for sweating, decent sunscreens don't sweat off. Where do you think the waterproof ones come from. The idea is you apply it at least 10 minutes before you go out into the sun so it soaks into your skin. That way it doesn't come off. So if you are commuting to work for example, just apply it before you have breakfast of something.

I'm no doctor, but my doctor said that the Reader Digest report was right! It appears perhaps no body really knows...as usual! But 15 to 20 minutes is not sufficient enough to burn the skin; even my wife who is a strawberry blond with very light complexion won't burn in 15 to 20 minutes.

You don't have to burn to get irreversable sun damage.

Oooh, my thymine dimers!

15-20 minutes isn't that long.
most people get more than that driving around in their cars.

I burn too easily not to use sunscreen and I also live north of the 45th parallel. My Dr. prescribes a 50,000 IU gel capsule of vitamin D that I take once a week.