The Basics

Ultraviolet Radiation

 UVB rays are high energy and are responsible for sunburn, while UVA rays are lower energy, are more constant year round, penetrate glass, and cause premature aging.  UVA rays also depress the immune system and are more linked to skin cancer, especially melanoma, than UVB.  In fact, UVA rays are more damaging to the skin than any other external factor, including smoking. During daylight hours, both UV rays are upon us when we are outdoors and UVA reaches us when we are sitting near windows.

Sun Protective Factor

The SPF rating is a measure of the time it would take you to sunburn if you were not wearing sunscreen as opposed to the time it would take with sunscreen applied. So, in theory, if you burn in 10 minutes without sunscreen, an SPF 30 would provide protection from burning for 30 times this duration, or 300 minutes (5 hours); an SPF 60 would protect you for 60 times this duration, or 600 minutes (10 hours). However, this is not the reality, and it is very misleading.

“SPF is not a consumer-friendly number,” says Florida dermatologist, James M. Spencer, MD. “It is logical for someone to think that an SPF of 30 is twice as good as an SPF of 15 and so on. But that is not how it works.”

Whatever product you choose, experts recommend reapplying sunscreen at least every two hours and after drying off from swimming or sweating. “The best way make sure you are protected is to reapply sunscreen often,” Spencer says. “You just can’t put it on in the morning and forget about it. I don’t care if it’s SPF 800 or the best UVA protection, after a few hours it’s gone.” Really, after just a couple of hours its effects are gone.

SPF refers to the ability of a sunscreen to block UVB rays, which cause sunburns, but it does not account for UVA rays, which are more closely linked to deeper skin damage and skin aging. Both UVA and UVB contribute to the risk of skin cancer.

Sure, sunscreens with higher SPF ratings block slightly more UVB rays, but none offer 100% protection. An SPF 15 product blocks about 94% of UVB rays; an SPF 30 product blocks 97% of UVB rays; and an SPF 45 product blocks about 98% of rays. So, an SPF 30+ sunscreen is not significantly more effective than one with an SPF of 30, though the numbers may suggest otherwise. As the American Academy of Dermatology (AAD or Academy) advises, Spencer recommends SPF 30 products to all of his patients.

Since SPF refers only to UVB blockage, and not UVA protection, an effective sunscreen must block UVA rays, as well. Look for the term “broad spectrum.” Chemical sunscreens absorb the sun’s rays. They can be irritating and sting the eyes. Physical sunscreens use ingredients to create a physical barrier that reflects UV rays. They are generally better tolerated on sensitive skin but can leave a white cast or streak, which can be aesthetically displeasing, and may not offer as much UVA protection compared to chemical sunscreens. Physical sunscreens are also a bit thicker so they can be more difficult to apply. Since each category has its pros and cons, many of today’s sunscreens contain both physical and chemical UV filters. Sunscreens labelled as “natural” have mineral ingredients and lack chemical ingredients. See link at end of post.

Amount Counts

If you do not use enough, you will not get enough protection. Here is a fun tip: the amount needed to cover your face and neck is about as much as as you would need to create a thick line the length of both your index and middle fingers.

Window Transparency

Protect yourself when you are sitting indoors near a window or inside a car, as well. Because you are at risk when in direct sunlight, even if you are indoors. UVA rays – the ones that cause skin to age and account for most skin cancers – penetrate home and car windows. Newer windows offer some UV protection, and additional tinting helps, but these measures certainly do not provide 100% protection.  They should not be a substitute for sunscreen and other sun protective measures.

Check out a great chart comparing physical and chemical sunscreens at Skinacea.