Those of us who are now middle-aged white people remember when SPF 15 was the maximum coverage product, and it was powerful. It even worked for the freckly kids who had to wear t-shirts over their bathing suits. If your skin tone allowed you to get a little tan, wearing SPF 8 was considered prudent.
Yet now, in 2019, it is impossible to find sunscreen with a protection factor of even ten. Below 15 SPF cannot be sold at CVS, everything is PABA-free, and rows of sun products with 50 SPF labels seem to be waiting primly for a spot in Miss White’s designer handbag.
Why the SPF 50 when 15 used to be just fine? What is PABA, and why must one be free from it? And what really happens to beams when they meet a cream?
SPF is only half of the protection story.
First, SPF, if you didn’t know, means “Sun Protection Factor,” and refers to time. If you could normally stay in the sun for a half hour without burning, but a cream lets you go burn-free for twelve, then its SPF would be 24, as in twelve times as long, i.e. the whole day. But SPF pertains only to burning, and does not indicate how safe you may or may not be from slower-cooking UV-A rays.
The SPF does not tell you about the other damage.
The sun protection factor indicates how long you are safe from UV-B radiation, which has shorter-wavelength, more powerful, beams. Since UV-A rays cause ageing and collagen damage, we also need to know about them. So…designer handbag people, beware: a high SPF might not repel UV-A rays at all.
Only sunblock prevents UV-A damage.
To achieve total shade from UV-A radiation, current products must find a way to block them. A sunblock (like zinc oxide) contains opaque pigments (chemically rendered invisible to the human eye) that reflect the light, preventing it from penetrating the skin.
But let’s go back to sunscreen. If sunblock is like a paint that blocks the rays, what is a sunscreen, and how does the screen part work?
When sunbeams meet sunscreen…
Many sunscreens work via an organic substance such as the bugaboo PABA – para amino benzoic acid- whose chemical structure is in sync with the sun’s radiation. A white powder before it’s added to a cream, PABA’s structures vibrate at the same frequency as the sun’s 280-320 nanometer UV-B rays (Field 8). The sun beats down on skin covered in a PABA cream, and the para amino benzoic acid molecule’s different electrons, held in a ring-like benzine structure connected to a carboxyl group, shoot back and forth. As it moves the electrons, the radiation expends its energy on the surface of the product (instead of penetrating to blood vessels beneath) and disperses back into the atmosphere as “gentle heat” (Emsley 23). Thus, the cream filters the sun’s radiation. Other chemical filters that work the same way include oxybenzone, camphor, and cinnamic acid, and their variants. They all contain a carbon grouping and so are called “organic.”
So what’s the danger with PABA?
Well, “tests on human cells showed that, while PABA itself did not cause cancer, it increased the formation of cancer precursors” (Emsley 24). Oh, and in 1% of cases, those who used PABA sunscreens became more photosensitive (24). Oxybenzone faces criticism now, too, but for slightly different reasons. Both still work for most people.
Only astronauts without space suits burn in seconds.
Interestingly, the human body’s natural defense is typically amino acids on the outer layer of skin. These absorb UV rays safely for a little while (Emsley 18), perhaps just enough time to use the sunlight to manufacture vitamin D. – AB
Emsley, John. Vanity, Vitality, and Virility: The Science Behind the Products You Love to Buy. Oxford University Press, 2004.
Field, Simon Quellen. Why There’s Antifreeze in Your Toothpaste: The chemistry of household ingredients. Chicago Review Press, 2008.
Shapiro, Nina, and Loberg, Kristin. Hype: A Doctor’s guide to medical myths, exaggerated claims, and bad advice- how to tell what’s real and what’s not. Saint Martin’s Press, 2018.
Stockton, Nick. “Big question: How does sunscreen shield your skin with science?” Wired Magazine, July 2015. www.wired.com/2015/07/big-question-sunscreen-shield-science/