SUNSCREEN MATTERS: SOME FACTS AND FIGURES
 
Sunscreen Realities:

Is sunscreen with an SPF rating of 60 twice as effective as one with an SPF rating of 30?  It’s marginally better, but not even close to twice as good.

The American Academy of Dermatology, recommends using a sunscreen with at least a Sun Protection Factor, (SPF) of 30 or higher: “Dermatologists recommend using a sunscreen with an SPF of at least 30, which blocks 97 percent of the sun’s UVB rays. Higher SPF numbers block slightly more of the sun’s UVB rays, but no sunscreen can block 100 percent of the sun’s UVB rays.”  The FDA and Harvard Medical School also agree that SPF 30 is the recommended minimum to use.

Note that SPF only measures protection from UVB radiation only. It does not measure deep-penetrating UVA radiation. There is no labeling system that informs users the level of UVA protection they’re getting (or not) in a sunscreen.

Something to ponder, Sunscreen with an SPF rating of 30 allows approximately 3 percent of UVB rays to hit your skin while a sunscreen with an SPF rating of 50 allows about 2 percent of those rays through. A one percent difference seems minimal until you consider that SPF 30 allows 50% more harmful rays in than does SPF 50.  Also consider that if you’re not applying enough sunscreen properly, the amount of ultraviolet rays penetrating to your skin is more than the SPF rating that you’re using.  Be generous!

The American Academy of Dermatology further reports that, “It is also important to remember that high-number SPFs last the same amount of time as low-number SPFs. A high-number SPF does not allow you to spend additional time outdoors without reapplication. Sunscreens should be reapplied approximately every two hours when outdoors, even on cloudy days, and after swimming or sweating, according to the directions on the bottle.”

Cyclists should use a broad band sunscreen (protects against both UVA and UVB sun rays) labeled as “water resistant” (effective for up to 40 minutes in water) or preferably “very water resistant” (effective for up to 80 minutes in water).  This means the sunscreen provides protection while swimming or sweating, up to the time listed on the label.

How much and when should you apply sunscreen:

• Apply enough sunscreen to cover all skin that clothing will not cover. Most adults need about 1 ounce — or enough to fill a shot glass — to fully cover their body. Harvard Medical School recommends, “applying sunscreen using the “teaspoon and shot glass rule”: 1 teaspoon of sunscreen to the face and neck, and enough to fit a shot glass (approximately 1 ounce) for exposed areas of your body.”
• Apply sunscreen to dry skin 15 minutes before going outdoors. Sunscreen needs to be absorbed into the skin to work effectively.  Remember that sunscreen is different from sunblock.  Sunblock is a physical barrier, usually opaque, that lays on the skin and forms a sun barrier.  Think lifeguards with white noses.
• Skin cancer also can form on the lips. To protect your lips, apply a lip balm or lipstick that contains sunscreen with an SPF of 30 or higher.

 
There is a ‘general’ formula to determine the SPF factor that you need to properly protect yourself:

SPF Number x Exposure Time Without Protection (how long it takes you to burn with no protection being used) = Minutes Protected.

Assuming the use of a sunscreen rated at SPF 15 and you sunburn after 10 minutes without protection:  15 x 10 minutes = 150 minutes of protection.

Remember that this formula assumes that you’re applying the proper amount of sunscreen with full coverage.  Furthermore, the FDA states that this formula is not always dependable.

There is a popular misconception that SPF relates to time of solar exposure. For example, many consumers believe that, if they normally get sunburn in one hour, then an SPF 15 sunscreen allows them to stay in the sun 15 hours (i.e., 15 times longer) without getting sunburn. This is not true because SPF is not directly related to time of solar exposure but to amount of solar exposure. (emphasis added).  Although solar energy amount is related to solar exposure time, there are other factors that impact the amount of solar energy. For example, the intensity of the solar energy impacts the amount. The following exposures may result in the same amount of solar energy:  one hour at 9:00 a.m. vs. 15 minutes at 1:00 p.m.  Generally, it takes less time to be exposed to the same amount of solar energy at midday compared to early morning or late evening because the sun is more intense at midday relative to the other times. Solar intensity is also related to geographic location, with greater solar intensity occurring at lower latitudes. Because clouds absorb solar energy, solar intensity is generally greater on clear days than cloudy days.

The FDA also considers that skin type, amount of sunscreen applied and reapplication frequency contribute to a sunscreens level of protection or non-protection.

Regarding spray-on sunscreen, the FDA has opined that those using spray-on sunscreen be sure to use generous amounts and to physically rub the sprayed-on lotion in (emphasis added) to insure appropriate coverage.  Simply spraying without rubbing it in can leave gaps the user will be unaware of. 

The FDA has determined that two main ingredients are “generally recognized as safe and effective” (GRASE):  Titanium dioxide and Zinc oxide, while two main ingredients are not GRASE:  PABA and Tolamine salicylate.  These non-GRASE ingredients should not be available in the US but be sure to check.  Should you have sunscreen with non-GRASE ingredients, the FDA recommends discarding them.

Regarding sunscreen/Insect repellant combination sprays and lotions, the FDA says that,

Sunscreen-insect repellent combination products are proposed as not GRASE. Incompatibilities between instructions for use for sunscreens and insect repellents prevent these products from being labeled in a manner that sufficiently ensures safe and effective use of the sunscreen component. There are also data suggesting that combining some sunscreen active ingredients with some insecticides may increase absorption of one or both components.

Sunscreen Expires:

The U.S. Food and Drug Administration (FDA) regulates sunscreen and it is considered an over-the-counter drug.  Guidelines state that sunscreen expires after three years.  Interestingly, not all sunscreen is sold with a printed expiration date so it is recommended that when purchasing or receiving sunscreen that isn’t labeled with an expiration date, you should write it on the bottle or tube for your protection.  Expired sunscreen itself won’t harm you, but you can certainly be harmed due to its inability to protect you.

Michael A. Katz
White Clay Bicycle Club
Safety and Education Committee Chairperson