Choosing a Sunscreen
When choosing a sunscreen there are three important factors to consider:
First, how much UVB coverage will you require?
Ultraviolet B rays are only present outdoors. They do not penetrate glass. However, they do reflect off many surfaces, such as snow, water, sand, and even cement, and you may be exposed to them whenever you are outdoors, even when wearing a hat or sitting in the shade. They are stronger in the summer and in the middle of the day, from 10 AM to 4 PM. The amount of protection a product gives you against UVB rays is indicated by the SPF number. If you are going to be out less than an hour total on a given day, a product with an SPF of 30 (or an SPF 15 product applied twice a few minutes apart) should be adequate. If you will be out for several hours, or for a couple of hours in the middle of the day, an SPF of 45 may be more prudent. If you plan activities on reflective surfaces (tennis, skiing, swimming,...) which may last more than a few hours, you should consider a sunscreen with an even higher SPF (70 is reasonable*).
*Why such high SPF’s? The average person applies sunscreen in a way that results in them having on their skin about half of the SPF listed on the bottle the moment they have applied it. (Sunscreen makers like high ratings and have their test subjects really pile it on.) Then, just by living (sweating a bit, touching your face, etc.) the SPF will begin to decline. So an SPF of 70 will typically actually be a 35 right after application and more like a 20 an hour or two later. The American Academy of Dermatology recommends an SPF of 30 daily for exactly that reason. SPF 15 is actually adequate, but applying 30 is the way to get an actual 15 on your face.
Second, do you need UVA coverage?
The only reasonable answer to this is yes. Unless you will spend the entire time that the sun is up in a windowless room, it is a good idea to choose a sunscreen that will help protect your skin from ultraviolet A rays. These rays occupy the wavelenths between visible light and more powerful UVB rays. In amounts put out by the sun, these rays do not burn or tan your skin. They do, however, penetrate more deeply into your skin and they also penetrate glass. So you are being exposed to UVA anytime you are in a room with a window, either at your home or office, when you are in your car, and, of course, when you are outdoors. These rays have been known for many years to be involved in the aging process, and if you’d like your skin to age well, with less wrinkles, fewer brown spots, and better elasticity, you definitely want to protect yourself from UVA. Unfortunately, these rays were discovered in the 1990’s to also be contributors to the development of melanoma, squamous cell carcinoma, and actinic keratoses. This is an even more important reason to protect your skin daily from too much UVA exposure.
Third, do you need a sunscreen that is water-resistant?
Despite some product claims, no sunscreen is waterproof. All wash off over time when exposed to sweat or water. Sunscreens which are labelled as water resistant maintain their SPF after 40 minutes in the water. Sunscreens which are labelled as very water resistant maintain their SPF after 80 minutes in the water. Towelling off after being wet will also remove quite a bit of sunscreen, so it is important to reapply after getting dry. Sunscreens which are water resistant tend to be a little less pleasant to wear than those which are not, and there is no need to wear them on days during which you will not sweat heavily or be getting wet. Do remember, though, that skiing in powder usually involves getting some snow spray and a water resistant sunscreen is a very good idea for those days, even if it is cloudy or snowing.
Finally - all sunscreens lose effectiveness throughout the day, so if you are outdoors, reapply every couple of hours.
Just as important as anything above: Find a sunscreen you like! No one will wear something they hate every day long term. Sunscreen is big business these days, and the market offers a multiplicity of products geared to many different tastes and needs. There is very likely something that is just right for you.
A great web site with excellent sunscreen information: