A few weeks ago, I took my daughter to the opening of an outdoor portion of our local children’s museum.  As a service, the museum provided sunscreen for all who attended.  Not just any sunscreen, but natural, “chemical-free” sunscreen.  Several women near me were chatting about how nice it was that the museum provided “chemical-free” sunscreen.

The chemist in me rolled my eyes.  Why?  Because everything is made of “chemicals.”  So, it is a bit of a misnomer to call this sunscreen “chemical-free.”

The words “contains organic ingredients” also highlight the difference between language used in marketing versus the scientific community as a whole.  The word “organic” has many meanings but is often associated with living (or once-alive) organisms.  In chemistry, “organic” simply means chemical compounds associated with living species, specifically, a carbon backbone. Thus in chemistry, organic simply means “containing carbon,” while in the marketing world, “organic” often means “limited pesticides.”

Now that that misnomer has been debunked, what you need to know is that in the sunscreen world, two labels are used to describe it: “mineral” and “chemical” sunscreen. “Mineral” sunscreens typically refer to zinc oxide and titanium dioxide, which are chemical compounds labeled “inorganic” because they do not contain carbon atoms in their overall structure.  Conversely, “chemical” sunscreens are made up of carbon-containing molecules that absorb light, and because they contain carbon, chemists refer to them as “organic.”

Below is the chemical structure for oxybenzone.  When an organic molecule has a lot of double bonds like you see below, it’s good at absorbing UV light, the same light that we are trying to block using sunscreen (absorbing in this case means the same as blocking). This is what makes oxybenzone a good sunscreen.

Chemi2

(Drawn using Chemdoodle, http://web.chemdoodle.com)

The green sunscreen shown above is the one given to us by the children’s museum, and it contains zinc oxide (ZnO), and titanium dioxide (TiO2). These are also chemicals, just a different type of chemical.  ZnO and TiO2 are not carbon-containing molecules (“organic”), but rather inorganic UV blockers.  Many sunscreen brands refer to zinc oxide and titanium dioxide as “mineral” sunscreens.  This term evokes thoughts of gathering rocks and grinding them up and plastering the mix on your body.  But this actually is a bit of marketing language.  Zinc oxide and titanium dioxide are also chemicals.  In fact, they’re chemicals not typically even found in nature, but rather created or synthesized in the lab by oxidizing zinc and titanium metal.

(Drawn using Chemdoodle, http://web.chemdoodle.com)

(Drawn using Chemdoodle, http://web.chemdoodle.com)

So what are the pros and cons of each type of sunscreen?

Pros and cons of oxybenzone sunscreen: Oxybenzone is a clear sunscreen, meaning that it is relatively easy to apply and does not have a white appearance. Most importantly, oxybenzone absorbs UV light and protects your skin from UV damage, which makes it a good sunscreen.  The drawbacks of the UV-absorbing organic compounds include a higher rate of allergic reactions in users and the possibility of the compound being disruptive to hormones such as estrogen. Although studies show that oxybenzone  does bind to estrogen, panic associated with this finding is unfounded.  In 2004,  a study that found that while humans absorb oxybenzone, there was not enough evidence to suggest that the absorption of oxybenzone affected hormone levels.  In my professional opinion, the benefit of oxybenzone protecting your skin from harmful UV rays outweighs the small risk that oxybenzone may be a hormone disruptor.

Pros and cons of Zinc oxide and Titanium dioxide sunscreen: Zinc oxide and titanium oxide sunscreens are also both very effective at blocking UV light from your skin through a combination of scattering and absorbing the UV light. However, the biggest drawback of zinc oxide and titanium dioxide is their cosmetic appearance.  Both of these compounds are white and produce an opaque appearance on the skin.  Even with advances of making ZnO and TiO2 particles very small (i.e. to make them more translucent), the opaqueness is still an issue for those who prefer invisible protection.

I personally use both types of sunscreen for myself and my children, so my recommendation?  Use sunscreen.  Any type that you can find or afford.  It would be much better to use any type of sunscreen than none at all – just make sure that your children are protected to prevent sunburns.

 


 

Resources

Burnett, M. E. and Wang, S. Q. (2011), Current sunscreen controversies: a critical review. Photodermatology, Photoimmunology & Photomedicine, 27: 58–67.

[2] Schauder, S.,  Ippen, H. (1997) Contact and photocontact sensitivity to sunscreens. Review of a 15 year experience and of the literature. Contact Dermatitis, 37, 221–232

[3] Janjua, N. R., Mogensen, B., Andersson, A., Jørgen, H. P., Henriksen, M., Skakkebæk, N.,E., & Wulf, H. C. (2004). Systemic absorption of the sunscreens benzophenone-3, octyl-methoxycinnamate, and 3-(4-methyl-benzylidene) camphor after whole-body topical application and reproductive hormone levels in humans. The Journal of Investigative Dermatology, 123(1), 57-61.

 

 

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Categories: Science 101 + Mythbusting