Sunscreen Beyond the Basics Part II: Sunscreen Safety and What You Should Avoid

13 May 2019

Have you read my last blog post Sunscreen Beyond the Basics: Controversies, Trends and FAQs About Sunscreen? There are a lot of issues and controversies surrounding sunscreen so this blogpost, part 2 of a sunscreen series that I will be writing about will cover some of the safety concerns and the latest news about sunscreens. Here’s a little teaser: Nope, not all sunscreen filters are entirely safe. Which one is it? I won’t spoil the fun, so read on : )


This blogpost will cover the safety issues regarding: –

1. Nanoparticles in sunscreen

2. Hormone or endocrine imbalance with sunscreen filters

3. Whether sunscreen use causes vitamin D insufficiency


I hope that you find this post useful! This post took longer than expected for me to write because of the sheer amount of fact checking and referencing that I had to do to make sure that the facts were as up to date as possible. Along the way, I learnt a lot; including which sunscreen filter I would avoid. I look forward to sharing more knowledge with you all : )


Nanotechnology and nanoparticles in sunscreen


Recent years have ushered in the trend of downsizing from smaller mobile phones to nanosized particles in skincare.

Nanoparticles are very fine particles (i.e. smaller than 100 nanometre- one nanometer is 0.000001mm).  Some skincare brands have incorporated nanotechnology in their sunscreens, especially for the physical (inorganic) sunscreen filters to overcome the white cast caused by application of physical sunscreen filters so that the cosmetic finish of the sunscreen is improved.


One of the worries is that these nanosized particles can be absorbed through the skin. However, the stratum corneum of our skin prevents the penetration of these nanosized particles1,2 so it is safe to say that these small particles do not get absorbed through the skin are safe for use and do not pose a health risk. Multiple studies have also confirmed this finding that nanosized particles in sunscreen are safe3-5 .

Image source and credit6


Nanosized zinc oxide or titanium dioxide particles are first manufactured as very small primary particles. These particles have a tendency to cluster together to form agglomerates because of the drying and heat treatment during the manufacturing process6. The agglomerates are much larger than nanoparticles and cannot penetrate the skin to cause any systemic toxicity.



Nanosized zinc oxide and titanium oxide are safe for use and may be a good option for people who prefer to use physical (inorganic) sunscreen filters but dislike the white cast caused by physical sunscreens.


Do sunscreens cause hormone or endocrine imbalance?


There have also been concerns that sunscreens can disrupt hormone balance and even cause cancer- these have been shared widely on various blogs, social media outlets and even Doctor Oz (who has also endorsed astrology and other miracle cures). Before we make sweeping statements or even unfounded statements about sunscreens, allow me to bring you through this controversies and the evidence behind these claims.


Some chemical sunscreens have been called ‘endocrine disruptors’ because some studies have shown that these chemical sunscreens can be absorbed through the skin and interfere with hormone levels in our bodies. The two sunscreen filters that have caused these concerns are oxybenzone and octinoxate. Let’s look at the data for each of these sunscreen filters.


Oxybenzone: A misunderstood tale

Most of these concerns for oxybenzone arose from a study conducted in 2001 with Oxybenzone and let me put some of the figures and data in perspective for you:


Oxybenzone is a chemical sunscreen filter that blocks out both UVA and UVB rays. It has been in use for over 50 years. The 2001 study that created anxiety about chemical sunscreen filters behaving as hormone or endocrine disruptors essentially showed that 21 day old rats fed supratherapeutic doses of sunscreen (yes, the rats were orally fed high doses of sunscreen)- 1500mg of oxybenzone daily and had a 23% increase in the weight of their uteri7. Note that these rats did not have sunscreen applied topically as most of us would use our sunscreens.


One of the biggest flaw with extrapolating this study to humans is that there is a huge difference between a human applying sunscreen and a rat consuming unnaturally large doses of sunscreen. So far, there is no data to show that oxybenzone causes major health problems in humans. In fact, oxybenzone has not been shown to accumulate in the blood even after days of topical application because oxybenzone is passed out in the urine8-10. To date, there is no study or data that shows that oxybenzone causes disruption of hormone levels or significant health problems in the body. In fact, there is a study conducted in humans that shows that oxybenzone does not causes significant hormone disruption even with topical application of 10% oxybenzone9. The US FDA has also approved the use of oxybenzone for adults and for children above 6 months of age.


Octinoxate/ Octylmethoxycinnamate: Possible cause for concern


Another chemical sunscreen filter that is widely used is Octinoxate. Octinoxate is also known as octylmethoxycinnamate (OMC). It has also been in the limelight because Octinoxate has been found to alter the hormone functioning in animal studies and this has been used as a clarion call for naysayers of the sunscreen camp to boycott the use of sunscreens.


The data surrounding the hormone disruption abilities of octinoxate from human studies is still limited– to date, there are only 3 studies that involved octinoxate being performed on humans (in vivo)8,9,11. Most of the what we know about octinoxate and its reported effects on hormones comes from studies on animals and human cells in the lab (i.e. in vitro). This important to note because what is most applicable and relevant would be studies performed on humans. If that is lacking, we will then have to extrapolate from results based on studies in animals and human cells (in vitro studies) within reasonable parameters.


So what does the data on octinoxate show? The studies on human beings (in vivo) showed a small but significant decrease in the levels of estrogen and testosterone9. There was no variation in the levels of thyroid hormones11. However, there were flaws with the study- the results were due to a natural biological variation and not to the application of octinoxate; short duration of the study and only one concentration was used9,11.


In the in vitro human studies performed, several of them showed that octinoxate had estrogenic potential7,12,13. Unlike the in vivo studies, the in vitro studies showed that octinoxate had  anti progesterone potential14-16 and anti-thyroid hormone activity17,18. With regards to testosterone, the in vitro studies did not show show an increase or decrease in testosterone levels, unlike in the in vivo human studies19,20.


In animal studies, octinoxate has been shown to exhibit some estrogenic activity,  with some of the animal subjects demonstrating an increase in thickness and weight of their uteri11,20. The exact mechanism by which octinoxate exerts its estrogenic activity has yet to be elucidated although it is hypothesised that the mechanism is different from the classic action of estrogen acting on the estrogen receptors.


Additionally, octinoxate has also been shown to display anti-progesteronic16,22 and anti-thyroid in animal studies23,24 just like the in vitro human studies. Animal studies also revealed anti-androgen (testosterone) activity14,24; but this was not proven in human studies.

Studies also have shown that octinoxate can possibly be found in the breast milk of nursing mums25,26. So far there are no studies conducted in babies for octinoxate, so if you are nursing mother, please take note of this!



Octinoxate does show some form of disruption of hormones, in humans and animals. There are not enough studies on humans to draw a link or a robust conclusion; so we will have to await for more studies and data. If you are concerned, then use sunscreens that contain filters than octinoxate.


Does Sunscreen Cause Vitamin D Deficiency? The controversy relating to “Is Sunscreen the New Margarine” article


A few months ago, an elderly patient asked me if sunscreen and sun avoidance could worsen her osteoporosis. Her orthopaedic surgeon treating her for osteoarthritis of her knee, in good nature, told her to soak up the sun for vitamin D. Fair enough I suppose, but do you know that vitamin D intake through sun exposure forms only one part of our daily total vitamin D requirement?


Fast forward a few months later to January this year, when this article titled “Is Sunscreen the New Margarine” was published and ignited a maelstrom of opinions. In his article, Rowen Jacobsen puts forth his opinion that sunscreen is bad for you because sunscreen application causes vitamin D deficiency.


This article quickly went viral and this prompted doctors and even the US FDA to put up statements and op-eds to rebut the non-truths in this article.


Is Sunscreen the New Margarine? Nope. So much for a clickbait title.


In his write-up, Rowen Jacobsen bases his case against sunscreen based on an unpublished study by one dermatologist, Dr Richard Weller and a single Swedish study by an obstetric research fellow that isn’t even about sunscreen. Jacobsen also casts basic biochemistry aside by neglecting to mention that vitamin D is a hormone manufactured by our bodies under the influence of sunlight and through our dietary intake of foods that contain vitamin D27. The reasons for vitamin D deficiency are (1) lack of vitamin D in the diet, often in conjunction with inadequate sun exposure; (2) diseases that affect vitamin D absorption through the intestines; and (3) kidney and liver diseases- enzymes in our kidneys and livers convert vitamin D to the biologically active form that it utilised by the cells in our bodies27.


One of the cruxes in this article that was never addressed by Jacobsen in his article, is whether sunscreen use causes vitamin D deficiency or other medical problems. Interestingly, Jacobsen does not offer any evidence to support his claim. Instead, he choose to makes his case for unfiltered, uncontrolled and unprotected sun exposure by making absurd correlations from the above mentioned Swedish study (that has a number of flaws) and an unpublished source.


Time and time again, the daily, consistent and long term use of sunscreens have been shown NOT to cause vitamin D deficiency and instead, protect against the side effects of sun exposure such as skin cancer28,29. There are a few reasons for this phenomenon and I will have to ask you to refer to my previous post Sunscreen Beyond the Basics: Controversies, Trends and FAQs About Sunscreen which explains some of the reasons why. As explained in my previous post, sunscreens do not block out 100% of UV rays and the majority of us do not apply adequate sunscreen (not to mention reapplication) to enjoy the full spectrum of coverage against UVA and UVB rays as advertised by our sunscreens.


The American Academy of Dermatology has also put up a statement that recommends an adequate amount of vitamin D should be obtained from a healthy diet that includes foods naturally rich in vitamin D (e.g., dairy products and fish), foods/beverages fortified with vitamin D (e.g., fortified milk and fortified cereals) and that increased sun exposure is not the answer to building up our bodies’ vitamin D levels30.


Rowen Jacobsen also quotes Australia’s stand on sun exposure: on days where the UV index is 3 or above- a few minutes of sun exposure a day is recommended. However, he has also neglected that in the same position paper from Australia, the recommendation is that this few minutes of sun exposure is done in combination with sun protection measures, including sunscreen31. Again, another misrepresentation from the article.


In essence, it is about striking a healthy balance between sun exposure for its numerous benefits (such as vitamin D synthesis; suppression of autoimmune diseases; and mood) and the risks that come with sun exposure (e.g. skin cancer and other skin related diseases). Although there is no current data or consensus on the amount of time that is considered to be acceptable for adequate sun exposure, Australia’s and the Cleveland Clinic’s recommendation is a few minutes to fifteen minutes a day through typical day to day outdoor activities31,32.


The controversial Swedish study by Lindqvist.

My other gripe with this article by Rowen Jacobsen is the bold and dangerous claims that he makes, such as: “Avoidance of sun exposure is a risk factor of a similar magnitude as smoking, in terms of life expectancy” based on the study by Lindqvist. To be honest, the findings intrigued me and I read the entire research study. In this Swedish study, the researchers administered questionnaires to 29,518 women from 1990 to 1992. The questionnaires looked at sun exposure habits, marital status, educational level, smoking, alcohol consumption and the number of births. The participants were followed up 20 years later and the study looked at development of diseases such as cardiovascular diseases and cancer as well as death. The authors concluded that participants with the most active sun exposure had a higher life expectancy and were at a lower risk of cardiovascular diseases (although they were at higher risk of skin cancer) compared to women who avoided the sun.


It is important to look at the validity of the study critically before we quote or extrapolate from them. The problems in this study? The researchers did not account for and control for proven risk factors of cardiovascular diseases and life expectancy such as diabetes; high blood pressure; family history of cardiovascular diseases and/or cancer; diet and exercise. This is very alarming for a study on cardiovascular diseases and life expectancy! The researchers also did not take into account sunscreen use despite measuring sun exposure habits. So for Jacobsen to take this flawed study which does not even take into sunscreen use to build a case against sunscreen is weak at best and outright misleading at worst.



Sunscreens do not cause vitamin D deficiency and intentional, unprotected sun exposure for vitamin D is not advised.



  1. Nanosized sunscreens are safe for use.
  2. Oxybenzone does not cause hormone disruption in humans.
  3. The data for octinoxate/ octylmethoxycinnamate and its effects on hormones in humans is very limited. Animal studies show that octinoxate/ octylmethoxycinnamate disrupt hormones. Avoid if you are worried.
  4. Sunscreen use does not cause vitamin D deficiency.
  5. Prolonged sun exposure to boost vitamin D levels is not recommended.
  6. A few minutes to fifteen minutes of outdoor day to day activities is adequate.
  7. Vitamin D can be obtained through food.

And there you have it, three pertinent safety issues about sunscreen safety! Another thing that I hoped that you have realised along the way is not to take studies/op-eds at face value. Sometimes, facts get misrepresented (deliberately or not) so always go back to the original studies and dissect them critically.


Have a good week ahead! I hope you learned a thing or two from my post for a healthier lifestyle:) Share the knowledge and please leave a comment if you have any questions or would like me to address a topic.

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In vitro and in vivo estrogenicity of UV screens. Schlumpf et al. Environ Health Perspect. 2001 Mar; 109(3): 239–244. 8. Sunscreens in human plasma and urine after repeated whole‐body topical application. Janjua. J Eur Acad Dermatol Venereol. 2008 Apr;22(4):456-61. 9. 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. Janjua et al.  J Invest Dermatol. 2004;123(1):57-6115191542 10. Percutaneous absorption of the sunscreen benzophenone-3 after repeated whole-body applications, with and without ultraviolet irradiation. Gonzalez et al. Br J Dermatol. 2006;154(2):337-34016433806 11. Sunscreens and thyroid function in humans after short-term whole-body topical application: a single-blinded study. Janjua et al. Br J Dermatol. 2007 May;156(5):1080-2. 12. Multi-organic risk assessment of estrogenic properties of octyl-methoxycinnamate in vivo: A 5-day sub-acute pharmacodynamic study with ovariectomized rats. Klammer. Toxicology. 2005 Nov 5;215(1-2):90-6. 13. Additive estrogenic effects of mixtures of frequently used UV filters on pS2-gene transcription in MCF- 7 cells. Heneweer et al. Appl. Pharmacol. 2005; 208: 170–177. 14. Effects of pre- and postnatal exposure to the UV-filter octyl methoxycinnamate (OMC) on the reproductive, auditory and neurological development of rat offspring. Axelstad et al. Toxicol. Appl. Pharmacol. 2011; 250: 278–290. 15. Comparison of effects of estradiol with those of octylmethoxycinnamate and 4-methylbenzylidene camphor on fat tissue, lipids and pituitary hormones. Seidlova-Wuttke et al.Toxicol. Appl. Pharmacol. 2006; 214: 1–7. 16. 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