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Sol Survivor: Shedding light on sunscreen ingredients Part 2 of 2

(This is the second in a 2-part guest post by Jen Phillips. Jen holds a PhD in biology and is a Senior Research Associate at Westerfield Laboratory Institute of Neuroscience at the University of Oregon.)

Making sense of sunscreen controversies

Hello again!  In Part I of this series of posts, we explored the science behind sunlight, sunscreen and skin cancer.  That post left us with some pretty compelling reasons to cover up and slather on, but in this continuation we’ll be examining a few common claims out there that suggest sunscreen isn’t all it’s cracked up to be and may, in fact, be bad for you.  To put your mind at ease up front, there are no legitimate health concerns associated with sunscreen use, and there are demonstrable health benefits to regular application. So what’s all the fuss about?  Let’s take a look:

Does sunscreen use prevent cancer?

At first, this might seem like a silly question.  UV rays causes cancer, sunscreen blocks UV rays, therefore sunscreen must reduce skin cancer, right?  Sure, but scientific evaluation to back up this conclusion has had some mixed results.

sunscreen 2The biggest and most well-designed study to date was conducted in Australia, beginning in 1992.  The study included over a thousand participants, divided into an experimental group who applied SPF 16 sunscreen daily for four years, and a control group who used sunscreen at their own discretion. Initial results were reported after the four-year testing period, and additional data were obtained by tracking participants in both groups for another decade.  Overall, the study showed clear benefit of daily sunscreen use in prevention of squamous cell carcinoma (SCC), a benefit in prevention of Melanoma that was only noted at the end of the 10 year follow-up, and only a slight, statistically insignificant benefit in prevention of basal cell carcinoma (BCC.)

Why weren’t the results more spectacular, you might wonder, given the obvious correlation between UV radiation and skin cancer?  Based on its prevalence, one could hypothesize that BCC is easier to trigger than the other forms of skin cancer, and thus the SPF 16 sunscreen did not block enough UV rays to significantly reduce BCC rates. It’s also possible that UVA rays play a role in triggering BCC.  When this study was initiated in 1992, the sunscreen provided to participants—and indeed, all sunscreens on the market at that time—were UVB blocking only.

Still, even imperfect protection is better than none at all, right?  So using sunscreen would seem like a pretty straightforward choice.  Nevertheless, recent concerns over the safety of the products themselves have complicated the picture.

Does sunscreen disrupt hormones?

This claim is specific to oxybenzone–an organic UV filter that has been an active sunscreen ingredient for over 40 years.  The worry stems from in vitro studies showing that oxybenzone influences expression of estrogens and androgens in cultured breast cancer cells.  A study using mice also showed hormone related changes in uterine tissue when animals were fed oxybenzone daily.  Further potential for concern came from reports of oxybenzone being detected in urine and breast milk.

While it all sounds scary, the Paracelsus maxim (“the dosage makes the poison”) is important to keep in mind.  In vitro studies are notoriously lousy at predicting effects in functioning, multicellular systems like humans.  Further, the mice in the oxybenzone study were fed massive doses of the compound.  It would take several hundred years of daily sunscreen application to achieve similar exposure in humans, so it’s unlikely to be an issue for most of us.

What about the levels detected in urine and breast milk?  Well, oxybenzone is a popular ingredient in lots of products and materials beyond sunscreen. As such, it’s not surprising that it’s detectable in human excretions, and it’s not unique in that regard.  The key questions here are: are those levels attributable to sunscreen use and, more importantly, are those levels harmful?   To the first question, the urine study found no correlation between sunscreen use and oxybenzone levels.  To the second, a number of human studies specifically testing whether oxybenzone exposure from sunscreen use had any physiological effects showed no significant problems.  And finally, irrespective of the source of exposure, there have been no health problems of any kind linked to oxybenzone.  While it’s definitely valid to continue to monitor the chemicals in our environment, it’s also important to note that in nearly 5 decades of widespread use, no safety issues have come up.

Does sunscreen cause cancer?

This concern is primarily based on some in vitro studies showing that retinyl palmitate can generate biologically reactive molecules when exposed to UV radiation.  Retinyl palmitate isn’t a UV filter at all, but rather a Vitamin A precursor molecule that is a common additive to sunscreen formulas, as well as a great many other skincare and food products.  The factors generated when retinyl palmitate is exposed to light, called free radicals or reactive oxygen species, have a well-known potential to induce cancer.

Again, this a reasonable thing to test, but of the numerous studies conducted to assess the carcinogenic potential of retinyl palmitate, only a minority showed an effect, whereas most showed no adverse outcomes at all.  When weighed against the fact that widespread use of retinyl palmitate for years has resulted in no health problems, the few small in vitro studies suggesting harm are not convincing.

An additional cancer concern was raised by a couple of small studies that showed an increase in Melanoma in low-SPF sunscreen users compared to non-users.  The methods of these studies were relatively poor, compared to others that showed either no difference or a protective effect of sunscreen use.  Importantly the researchers didn’t evaluate other potential causes for the increase in Melanoma that they observed.  Stacked up against the better methodologies of larger studies, most particularly the comprehensive Australian study mentioned above, the data just don’t support a causative link between sunscreen use and Melanoma.

Is sunscreen toxic?

This concern arises from recent modifications to the inorganic sunscreen ingredients, zinc oxide and titanium dioxide, both of which filter UVB and some UVA rays.  Zinc oxide has been around for a while—you’ll probably recognize it as that opaque white stuff that beachgoers slather all over their noses.  Titanium dioxide is a more recent addition to the sunscreen arsenal, but is similarly pasty in appearance.

While such products are well-suited for small, high profile areas like the nose and cheekbones, their thick, pasty formulas are so difficult to spread that they’re not generally used for whole body protection, which is unfortunate because in addition to being great UV filters they’re also far less likely to cause skin reactions or allergies than some of the organic compounds.

To get around this problem, recent formulations use microsized” or “nanosized” titanium dioxide or zinc oxide mineral particles.  These preparations have the dual advantage of making the product easier to spread and less opaque.   However, the small size of these particles has raised concerns about their ability to penetrate the skin and reach toxic levels in the living cells beneath.  Fortunately, all the evidence indicates that these particles aren’t able to enter the body through the skin. Most were even tested on broken skin and showed no tendency to penetrate to the living cell layers.  This seems to be due, at least in part, to the fact that although the individual particles are indeed very small, they tend to aggregate together in solution, forming chemical bonds that keep them from moving around independently.

swing-1Does sunscreen cause vitamin D deficiency?

This concern seems reasonable on its face. Skin cells in the epidermis produce a vitamin D precursor that is activated by sunlight (by UVB rays, specifically). Block the sunlight, and you could potentially block vitamin D synthesis.  Studies have shown that sunscreen can indeed reduce vitamin D production.  Vitamin D screening is common in primary health care, and is now a cornerstone of the supplement industry, as well as a popular scapegoat for a wide range of maladies in the ‘wellness’ community.

There is a great deal of variation in the definitions of what might constitute a clinically normal vitamin D level in adults, so much so that experts don’t actually recommend routine screening at all.  However, legitimate vitamin D deficiency can lead to some well-characterized developmental problems, like rickets, so it is important to do due diligence when considering the effect of sunblock for children.  Fortunately, research has shown that the use of sunscreen doesn’t contribute to vitamin D deficiency.

Why the discrepancy? In short, it seems that no one is perfectly compliant when applying sunscreen.  A little sun exposure, literally 15-30 minutes a week, is all an otherwise healthy fair skinned person needs to synthesize sufficient amounts of vitamin D.  A few minutes in the sun without sunscreen, or maybe just on that one spot you couldn’t quite reach, appears to be enough.  This is borne out by both the lack of correlation between sunscreen use and vitamin D deficiency, and also the low incidence of rickets and other known outcomes of vitamin D deficiency, in the sunscreen-using population.

Are spray-on sunscreens safe?

A couple of years ago, the FDA announced that it was collecting more data on spray-on sunscreen, which at the time was relatively new to the market.  This was interpreted as an ominous development by some, and a number of unofficial advisories were issued about avoiding use on children, risk of inhalation, etc.  The FDA didn’t issue any sort of follow up on their findings, but based on the number of consumer bulletins about spray-on sunscreen on the FDA website, it seems pretty clear that there are no specific health concerns regarding the sunscreen part of the ingredients.  Much more emphasis has been placed on regulating the ‘dosage’, if you will, since it is applied so much differently than sunscreen lotion.  There are also a number of common-sense precautions that also apply to many other spray-on products. For example, it’s a terrible idea to apply an alcohol-based spray around an open flame, no matter what the other ingredients are.  It’s probably not a good idea to spray sunscreen into your kid’s face, any more than it would be a good idea to spray insect repellent or hairspray.  Inhaling aerosol products in lieu of air is typically an unpleasant experience.  However, aside from these fairly broad safety guidelines, there isn’t any specific reason to shy away from spray on sunscreen.

In summary,

-sunscreen continues to be recommended by healthcare professionals to prevent burns as well as to protect skin from premature aging and from cancer.

-sunscreen safety has been well established.  No health issues have been linked to sunscreen ingredients, despite extensive testing.

-sunscreen provides maximum protection when used appropriately—applying a thick, even layer and reapplying regularly.

One last thing:  the FDA requires sunscreen to be tested for stability and durability, and the expiration dates are usually around 3 years from the date of manufacturing.  These dates are backed by sufficient testing so as to be trustworthy, but also require the liberal application of common sense.  If your sunscreen is stored in extreme temperatures for a long period, for example, or if it changes consistency from one year to the next, it’s a good idea to replace it even if it’s not technically expired.

So, be smart about sun exposure, wear hats and water shirts when possible, seek out a broad-spectrum product with high SPF, slather up, and have a beautiful summer.  I’ll see you at the pool.


For more tips and information, see this sunscreen FAQ from the Skin Cancer Foundation

Also, see the Skin Cancer Foundation’s response to some of the recently renewed claims.



Burnett and Wang, 2011. Current sunscreen controversies:  a critical review. Photodermatology, Photoimmunity & Photomedicine. 27, 58-67

Jansen, et al., 2013. Photoprotection: Part II. Sunscreen: Development, efficacy and controversies. Journal of the American Academy of Dermatology 69(6). 867.e1-867.e14.

LeFevre, et al., 2015. Screening for Vitamin D Deficiency in Adults: U.S. Preventative Services Task Force Recommendation Statement.  Annals of Internal Medicine.162(2): 133-140.

Green, et al., 2011. Reduced melanoma after regular sunscreen use: randomized trial follow-up. Journal of Clinical Oncology  29(3):257-63.

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Sol Survivor: Shedding light on sunscreen ingredients Part 1 of 2

I’m very excited about this post for two reasons. One: it’s the first time I’ve recruited a guest blogger to write for It’s MomSense. This is cool to me because it means someone thinks my blog is influential enough to take their own (unpaid!) time to research and help us parents wade through the misinformation running rampant in parenting circles. The second reason is that this is a topic that I have meant to look into for some time. I am very fair skinned and burn easily and I’ve managed to pass this trait on to my red-headed son. I feel like I’ve spent every summer since he was born running around after him with a tube of sunscreen and a hat. Every once in a while there’s a small voice in the back of my mind asking if I’m actually doing him a disservice by routinely rubbing chemicals into the skin on the back of his neck. As a result, a while ago I added “sunscreen ingredients” to my running list of things to research and blog about.  Now that summer is in full swing and the sunscreen and I are best buds again, I’m glad to check this one off my list.

Because this topic is pretty involved, we decided to split it into two posts. So today and next week you’ll be hearing from Jen Phillips instead of me! Jen is the mom of two kids (one teen, one darn close) who has a PhD in biology.  She is a Senior Research Associate at Westerfield Laboratory Institute of Neuroscience at the University of Oregon. There she uses zebrafish to study the molecular genetics of human diseases. When she’s not hunkered down in a dark microscopy lab, she likes to romp in the sunshine with her family and dog. Jen plans to start her own blog at some point this year under the name Clutch Science. For now, you can follow her on twitter @ClutchScience. Here’s Jen to shed some light on sunscreen ingredients. Hope you enjoy. -Sara

Part 1:  The dark side of our closest star

Confession time:  I love the sun.  Swimming, running, working, reading, eating, lounging, it’s all better done outdoors, as far as I’m concerned.  But, as a fair-skinned woman, and mother of two lightly pigmented kids, I’d be foolish to ignore the risk involved, or to fail to take preventative steps to keep us healthy.  I am a stickler for sunscreen use, and, much to the chagrin of my children, I will not hesitate to halt a fun outdoor activity if it’s time to reapply.

It’s not news that sun protection is an important part of preventative health.  Ultraviolet radiation damages skin in a number of ways, the most serious of which can lead to cancer.   Recently, though, concerns about sunscreen ingredients have made headlines, raising questions about whether sunscreens are effective at skin cancer prevention and even whether the use of sunscreen carries inherent health risks.   **Spoiler alert:  sunscreen is safe and effective and you should use it with confidence.  If you’re interested in knowing more about the basis for the concerns and why you don’t need to worry, though, please read on!**

In the first of this two-part series, I’ll outline a bit of the biology and strategic chemistry behind the interactions with our closest star, in order to set the stage for discussing the most popular current controversies in Part II.

UV radiation:  what’s in a wavelength?

UVA_UVB raysUV radiation occupies the electromagnetic spectrum between visible light and x-rays.  The UV portion of the spectrum can be divided into quite a few subcategories, but the two that we’re most concerned about in sun exposure are known as UVA and UVB rays. UVB rays (also known as “burning rays”) can’t penetrate beyond our epidermis, or outer skin layer.  In addition to causing sunburn, DNA damage to epidermal cells by UVB rays is a driving factor in the development of skin cancer in light skinned people.  Until recently, UVA rays were alternatively called “Tanning rays” or “Ageing rays” depending on what product was being marketed.  In contrast to UVB rays, UVA rays penetrate more deeply, through the epidermis to the dermis below.  UVA rays cause inflammation and damage to structural proteins in the dermal layer, which have historically been associated with wrinkles and saggy skin.  More recently, UVA radiation has also been implicated in DNA damage that can lead to skin cancers.  This reclassification led the FDA to upgrade its caution on the use of tanning beds, by the way, which use primarily UVA wavelengths and were often advertised as a ‘safe’ form of tanning before the carcinogenic potential of UVA rays were better understood.  Now that we know better, let’s talk about skin cancer.

Your epidermis is showing

Cancer of any type arises through DNA mutations that alter cellular behavior.  UV radiation has been used in laboratories to induce mutations in cells for nearly a century.  Our skin is exposed to UV radiation on a regular basis, and while the pigments in darker skin offer protection against cell damage, those of us with fair skin have an increased risk of skin cancers as a result of sun exposure.

All skin cancers originate in the epidermis, which is composed of a tightly packed basal cell layer and a more mobile layer of cells known as squamous cells.  Our skin sheds and renews itself regularly, so the epidermis is constantly cranking out new cells that progressively travel from deep in the epidermis up toward the surface, changing shape as they go.

Skin cancers are classified into three broad categories according to the cell type affected:  Basal cell carcinoma, Squamous cell carcinoma, and Melanoma. Genetics and environment influence susceptibility, but in light-skinned people, sun exposure is a major risk factor for all three types.


Basal cell carcinoma (BCC) is the most common form of skin cancer in people of European and Hispanic descent, with nearly 3 million cases diagnosed each year.  It is also the most benign, as it rarely spreads to other cells beyond the original tumor site.

Squamous cell carcinoma (SCC) Is the most common form of skin cancer in dark-skinned people (who have a lower incidence of skin cancer overall because of the protection of higher melanin levels in their skin) and the second most common form in light-skinned individuals.  About 700,000 cases are reported each year.  SCC can be disfiguring if left untreated, and can, more rarely, spread to other regions of the body.

Melanoma, a cancerous overgrowth of melanocytes, accounts for only 2% of all skin cancers overall, but has the highest death rate of them all.  Melanocytes, which produce skin pigment, are found in the basal cell layer of the epidermis, but their developmental origins and cell biology are distinct from the other cells in this layer.  These differences, which amount to different gene regulation for things like cell division and migration, contribute to the uniquely aggressive nature of malignant melanomas.

Considering the varied ways that things can go wrong in living skin cells, it’s important to understand what preventative steps we can take.  Limiting sun exposure during the peak hours is always a wise recommendation, as is the use of hats and clothing to cover the most exposed areas. But as lots of outdoor activities aren’t compatible with those guidelines, protection that can be applied directly to the skin is a great advantage.

How does sunscreen work?

All available sunscreen products contain UV filters that absorb, reflect, or diffuse UV radiation.  Ingredients with these properties are classified as either organic (carbon-based), or inorganic (based on other elements).

Lots of chemistry goes into choosing compounds that make the best sunscreen ingredients.  Compounds are tested for the particular range of UV wavelengths they can intercept and for durability.  The best compounds will block a wide swath of the UVB spectrum without being easily degraded.  No one wants to wear sunscreen that has to be reapplied every 15 minutes, right?  These qualities must then be weighed against the utility of the ingredient in a product designed to be applied to human skin:  Does it stink? Does it have a texture or color? Does it irritate skin or cause allergies?  Are there other safety or toxicity concerns?  FDA approval is required for all sunscreen ingredients, and their standards for safety testing are quite rigorous.  In fact, a number of organic sunscreen ingredients approved for use in Europe haven’t made the grade as far as the FDA is concerned.

What about SPF?

Sun Protection Factor of a product, or SPF, is usually framed for marketing purposes as the amount of time you can spend in the sun before burning when using the product versus time spent in the sun without it.  More specifically, the SPF value is the quantifiable effectiveness of the UVB filtering capacity of any given ingredient—or combination of ingredients. This is a non-linear numerical scale.  An SPF of 15 corresponds to blocking about 94% of UVB rays, while an SFP of 30 increases blocking capacity to 97%.

Note that SPF rates the product’s effectiveness of blocking only UVB rays. Since learning more about the damage that UVA rays can create, Sunscreen formulas have expanded to include UVA filtering alongside UVB (SPF-rated) protection.  Again, there’s a bit of a difference between how we do things in the US vs. abroad.  Other countries have a rating system (out of 5 stars) to indicate the strength of the UVA blocking compounds.  The FDA hasn’t implemented any such system yet.  The presence of UVA filters added to the SPF-rated UVB compounds in US products isn’t quantified, and only the words “broad spectrum” let you know that your sunscreen contains both UVA and UVB blocking ingredients.

To sum up this overview of the science behind sunscreen, both UVA and UVB rays can have detrimental effects on the health of your skin, so in addition to limiting exposure in as many ways as are practical, having a good sunscreen product on board is essential.

However, for the past several years a number of controversial warnings about the safety and effectiveness of sunscreen products have emerged.  In Part II of this series, I’ll examine those claims one by one to determine if there is really cause for concern.

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