Oh, how we Americans love convenience. We eat in our cars, watch movies on our phones, and have more “friends” on Facebook than in real life. So it’s no wonder that spray sunscreens like Neutrogena Ultra Sheer Body Mist Sunscreen SPF 45 ($11.95, Amazon.com) have been flying off the shelves. You don’t even have to get your hands dirty! Just point, shoot, and bam! You’re done!
But just as fast food consumption can lead to love handles, fast sunscreen application may cause health problems as well. At least one small study has shown a higher level of UV protection with lotion than with spray (source).
So we decided to test whether lotion or spray sunscreen is more effective for the average user. The results were astounding! But, to better understand the study, it’s helpful to know how SPF is determined in the first place.
How SPF is Determined
When scientists are formulating sunscreen, they are required to determine the SPF rating by applying 2 milligrams of formula per square centimeter of skin. That’s like applying a quarter tsp to your entire face.
Next, the skin is lit with a light with a known UV intensity.
Third, researchers measure to what degree different wavelengths of light cause sunburn. “Sunburn” here is a very loose term. In reality, researchers use precise methods in spectrophotochemistry to measure exact amounts of redness and swelling, called “erythema” in medical terms.
Lastly, these measurements are plugged in to an equation, from which SPF is determined.
where is the solar irradiance spectrum, the erythemal action spectrum, and the monochromatic protection factor, all functions of the wavelength . The MPF is roughly the inverse of the transmittance at a given wavelength.
Our Testing: Spray Sunscreen is About Half as Effective
The issue with spray sunscreen is not how much you are applying, as with lotion. Instead, the problem is for how long you are applying the formula.
If you apply a spray sunscreen for 2-3 seconds, you only apply about 0.5 milligrams per centimeter of skin, according to our in-house testing. [We measured this by measuring the forearm area and weights of bottles before and after application of spray sunscreen.] That means you get about one-quarter the protection you need to obtain the level of protection indicated by the SPF rating on the bottle. If you are applying a product with an SPF rating of 45, you would be getting SPF 10-12 protection. Not cool.
If you apply a spray sunscreen for double the time – 4-6 seconds – you’re faring much better: You get one-half the protection you need to achieve the level of protection indicated by the SPF rating on the bottle. So if you are applying a product with an SPF rating of 45, you would be getting SPF 22-25 protection. This is on par with the level of protection you get from the average lotion sunscreen (British Journal of Dermatology, 2001).
To apply enough lotion sunscreen to achieve the level of protection listed on a bottle, you need a 1/4 teaspoon for your face and neck, reapplied every four hours. The average person who uses sunscreen daily applies only half of this amount (British Journal of Dermatology, 2001), and even less on their body.
To apply enough spray sunscreen to achieve the level of protection listed on a bottle, our testing shows you need approximately six seconds of application per area of your body. The average user in our testing applied only 1/4 of the amount they needed, zipping over entire areas of their bodies in a mere 1-2 seconds.
We don’t want to definitively state you need to apply spray sunscreen for six seconds. However, this is what our testing suggests. In the future, we hope that this post encourages spray sunscreen manufacturers to do their own in-house testing to calculate and inform customers of exactly how long a formula should be sprayed over an area on the directions. For now, I personally am sticking to six seconds – or a cream formula!
One last note: Some sunscreen is better than no sunscreen. Any dermatologist will tell you this, as do studies of intermittent and imprecise sunscreen users (American Academy of Dermatology, 2000). That said, if you truly want an SPF 45 sunscreen to give you maximal benefits, you should apply the proper amount. And that is approximately a 1/4 tsp of lotion for the face, or six seconds of a spray sunscreen over a specific surface area.
What are your thoughts? Let us know in Comments!
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