Paperview: Sunscreen application to the face persists beyond 2 hours in indoor workers

What happens to your sunscreen throughout a work day? I often get this question, especially from people who work inside for most of the day. A group of researchers at Mahidol University in Thailand did an experiment that may provide us with some guidance.

The researchers took 20 people (15 women) with mostly skin phototype III and up. Skin phototype III means that they tan, but sometimes get mild burns.

The participants were asked to apply 1 gram of sunscreen to their face. The sunscreen was mixed with a blue fluorescent dye that would glow under UV light. This glow allowed the researchers to see the sunscreen on the skin and note changes in its brightness throughout the day.

The people only wore the sunscreen and were asked not to reapply. They weren’t allowed to use makeup or other skincare. They were also allowed up to 1 hour outside. The temperature outside was between 23 and 35 degrees Celsius throughout the day and described as humid. The indoor condition was inside the air conditioned Siriraj Hospital.

Every 2 hours, the researchers took a photo of the people and measured the glow of the sunscreen under a UV light. They looked at the cheeks, forehead, nose, moustache area, and the chin. They used a Visia device to help make sure the photos were consistent.

Sunscreen brightness reduction every 2 hours by percent. The bars indicate the range in measurement values.

The researchers found that the fluorescent glow on the people’s faces decreased the most in the first 2 hours after applying the sunscreen. On average the areas of the face were 16.3% less bright.

Between 2 hours and 4 hours after application, the brightness decreased by a further 7.4 percentage points on average. Between 4 hours and 8 hours, there was an average 4.5 percentage point decrease in brightness.

At the end of the day, there was about a 30% decrease in brightness on average compared to just after applying the sunscreen.

A 30% decrease in brightness in this experiment doesn’t necessarily mean a 30% decrease in sunscreen on the skin. There are ways to model this more accurately, but they did not have the tools in this experiment.

So what does this mean for you? At the end of the day, you’ll still have to use your best judgement.

If you pigment easily, are very concerned about photoaging, or have a family history of skin cancer – I think the best recommendation is to be on the safe side and reapply at least once around 2 hours.

If don’t care that much, consider the opposite, about 70% of the glow from the sunscreen still remained after 8 hours.

In either case, that first application is important. I’d recommend choosing a sunscreen with a high SPF and UVA protection and aiming for a 2 mg/cm² layer. An easy way to make it more likely you’ve applied that amount is to apply your sunscreen in two layers.

Source: Rungananchai, C., Silpa-archa, N., Wongpraparut, C., Suiwongsa, B., Sangveraphunsiri, V., & Manuskiatti, W. (2018). Sunscreen Application to the Face Persists Beyond 2 Hours in Indoor Workers: An Open Label Trial. Journal of Dermatological Treatment, 1–14. doi: 10.1080/09546634.2018.1530440

Paperview: Evaluation of the protection of a broad-spectrum SPF50+ sunscreen against DNA damage

Cyclobutane pyrimidine dimers (CPDs) are a form of DNA damage that is caused by UV exposure. CPDs interfere with base pairing during DNA replication – which can lead to mutations and cancer.

UVB radiation is directly absorbed by DNA. The energy causes changes in the bonding of pyrimidine structures found in DNA leading to CPDs and pyrimidine-pyrimidone (6-4) photoproducts.

UVA on the other hand is poorly absorbed by DNA, but was also found to cause CPD formation in human skin. CPDs were found to remain longer in the skin when there was UVA exposure, leading to speculation that UVA may also suppress a repair mechanism.

Our cells do have DNA repair capabilities, where damaged DNA is excised and replaced – but these processes can be overwhelmed by an accumulation of damage.

Experiments have measured the amount of CPD formation in human skin when exposed to UVB. One study found that CPDs were formed even when there was no visible sunburn (0.5 sunburn dose). They also found CPDs in both the epidermis and dermis and these levels were elevated for about 10 days as the skin sloughed off.

These two images from the paper show (A) skin that was not exposed to UVB and (B) skin that was exposed to UVB. The brown staining of the cells indicates presence of CPDs.

The amount of CPDs found in both the epidermis and dermis increased as UVB exposure increased.

A recent experiment performed by Pierre Fabre (manufacturers of Avène) looked at the effect sunscreen had on the  formation of CPDs in human skin after UV exposure.

14 volunteers applied a sunscreen to their forearm and were exposed to UVB and UVA on skin protected by the sunscreen and also on unprotected skin. The area covered in sunscreen received 15 times the dose of UV to cause sunburn, whereas the unprotected skin received 2 times the dose.

After this exposure, their skin was blistered by vacuum and the contents of the blister were examined for CPDs using two different methods: immunostaining and spectrometry (HPLC-MS).

They found that the unprotected skin after exposure to UV had an elevated ratio of CPDs to normal DNA bases (90 CPD to 106 DNA bases). In comparison, the skin protected with the sunscreen had an amount of CPDs similar to unexposed skin and statistically significantly less than the unprotected skin (P < 0.001) – even though the area received more UV exposure. The CPD to normal DNA base ratio was not reported for the sunscreen protected and unexposed skin.

The sunscreen was not named, but it is SPF 50+, broad spectrum, and contained; Tinosorb M and S, Iscotrizinol, Avobenzone, and the antioxidant bis-ethylhexyl-hydroxydimethoxy benzylmalonate.

Preventing the formation of CPDs from reducing UV exposure is the most well-researched option, but there are other newer methods that are emerging – some of which are already available on the market.

Photolyase is a DNA repair enzyme that can be activated by the absorption of a photon and transfer an electron to the CPD, this can separate the CPD back into two normal pyrimidine bases – with the right timing. In humans, the photolyase enzyme no longer works, but there is some evidence that topical application of photolyase may reduce the formation of CPDs. An experiment where photolyase encapsulated in liposomes combined with light exposure was applied to human skin reduced the formation of CPDs by 40%-45% after exposure to UVB.

You can watch a lecture given by Aziz Sanzar about photolyase and DNA repair below. He won the Nobel Prize in Chemistry in 2015 for his work along with his colleagues Tomas Lindahl and Paul Modrich.

S.K. Katiyar, M.S. Matsui, H. Mukhtar, Kinetics of UV light–induced cyclobutane pyrimidine dimers in human skin in vivo: An immunohistochemical analysis of both epidermis and dermis, Photochemistry and Photobiology (2002), DOI: 10.1562/0031-8655(2000)0720788KOULIC2.0.CO2
J. Gwendal, T. Douki, J. Le Digabel, et al, Evaluation of the protection of a broad-spectrum SPF50+ sunscreen against DNA damage, Journal of the American Academy of Dermatology (2018), DOI: 10.1016/j.jaad.2018.05.570

Should you avoid sunscreens with Avobenzone?

I’ve received quite a few questions about the organic sunscreen chemical Avobenzone over the years and I wanted to shed some light on one of the most common concerns – its photodegradation in UV. These concerns are usually raised by websites that say things like, “Avobenzone degrades in the sun, resulting in the release of free radicals that may actually increase the risk for cancer.”

What these quotes often leave out is the context, which is important in understanding why Avobenzone is so commonly used in sunscreens and why it is effective.

Avobenzone or butyl methoxydibenzoyl methane is an organic sunscreen that absorbs in the UVA region and has global approval. Among the sunscreen chemicals available in the US it is the strongest and most effective UVA absorber. Avobenzone exists in two chemical forms when in solution, the enol form and the diketo (or keto) form.

When exposed to UV light some Avobenzone in the enol form can be changed into the keto form – however this is slowly reversed once Avobenzone is removed from UV light.

In its keto form Avobenzone is susceptible to photodegradation from UV light. The energy from UV light causes structural changes in the Avobenzone that can lead to breakdown products. In many cases, those breakdown products no longer effectively absorb UVA and UVB (some of them will absorb UVC). Some of these breakdown products are also thought to be irritants. The other concern is that some singlet oxygen can also be formed – a reactive oxygen species which can damage DNA and cells.

The above only relates to Avobenzone on its own though, the material that Avobenzone is dissolved into and other chemicals in the formula can change how easily Avobenzone photodegrades. Other modifications like encapsulating Avobenzone have also been tested, though the benefit is often reduced contact between Avobenzone and the skin – not photostability.

Photostabilizers generally work by absorbing energy from the Avobenzone before it becomes unstable and breaks and down. Effective photostabilizers will then be able to take this energy and dissipate it in safer forms, most often heat.

A company that produces Avobenzone, DSM Nutritional Products, performed a study testing different photostabilizers and their effect on Avobenzone’s phostability. The most commonly used and known photostabilizer of Avobenzone is the organic sunscreen chemical Octocrylene, but there are other photostabilizers that don’t act as sunscreens such as Polyester-8 and Polysilicone-15.

To perform the test, 4% Avobenzone and different photostabilizers were dissolved into a mixture of 70% ethanol, 15% caprylic/capric triglyceride, and 15% C12-15 alkyl benzoate. The solutions were placed on glass slides at a density of 2 mg/cm2 then exposed to 25 MED (Minimal Erythemal Dose, 1 MED defined by the US FDA as 200 Joules/Meter2) units of UV light. After exposure, the amount of Avobenzone remaining was determined.

What the researchers found was that the combination of 4% Avobenzone and 3-5% Octocrylene maintained 90% of the Avobenzone after 25 MEDs of UV light. Based on this, they tested different combinations of Octocrylene and other photostabilizers to see how well they stabilized Avobenzone.

They found that 3.6% Octocrylene with 4% Bis Ethylhexyloxyphenyl Methoxyphenol Triazine or 4% 4-Methylbenzylidene Camphor were able to completely stabilize the Avobenzone after 25 MED of UV.

There’s currently no global standard on photostability, different regions have their own standards. In the US as part of the Broad Spectrum test, sunscreens are pre-irradiated with 4 MED before testing.

Just like how some chemicals can increase the photostability of Avobenzone, others like Octinoxate (Octyl Methoxycinnamate) are known to speed up the photodegradation of Avobenzone. This paper is often misquoted to include Oxybenzone (2-Hydroxy-4-Methoxybenzophenone), often mischaracterized as not photostable, as a chemical that increases the photodegradation of Avobenzone, but it was included as an internal standard to allow comparison between samples – as it did not photodegrade in the experiment.

What matters when it comes to the protection offered by a sunscreen are the values and ratings determined from standardized tests like SPF, PPD, Broad Spectrum, etc and not the appearance of an ingredient on the INCI.

Basing assumptions on INCI is dangerous, as the only way to truly know is to test the products. An experiment on 6 different commercial sunscreens on their photostability highlights this. 4/6 of the organic sunscreens tested exhibited a decrease in photoprotection after UV exposure. Of the two photostable organic sunscreens one contained a combination of Avobenzone and 4-Methylbenzylidene Camphor and the other Octocrylene, Avobenzone, Mexoryl SX, and Titanium Dioxide. The one inorganic sunscreen tested was shown to be photostable after UV exposure.

Keep in mind, this study tested commercial sunscreens available in 2006, where photostability was a relatively newer concern for sunscreens and standards had not yet been defined. It was around this time that Neutrogena began marketing its Helioplex patent, a photostable combination of Avobenzone, Diethylhexyl 2,6-Naphthalate, and Oxybenzone. The Helioplex US patent was granted in 2002 and other patents for increasing photostability of Avobenzone are present as early as 1999, when the US FDA finalized the use of Avobenzone in sunscreens.

While we still do not have a global standard for photostability, the options for and knowledge to stabilize sunscreens has grown considerably. It also still very important to reapply your sunscreen throughout UV exposure, this compensates for any protection lost through photodegradation as well as physical changes in the film of sunscreen on the skin.

Source: C. Mendrok-Edinger, K. Smith, A Janssen, J. Vollhardt. The Quest for Avobenzone Stabilizers and Sunscreen Photostability, Cosmetics and Toiletries,

Everybody’s free to wear sunscreen

You’ve probably seen this photo of a man who received chronic UV exposure on the left side of his face over the course of 28 years working as a truck driver. While this shows the effect that UV has on the skin, what’s important to keep in mind is that windows only block UVB light whereas UVA is often passed through.

Chronic UVA exposure can result in thickening of the epidermis and stratum corneum, as well as destruction of elastic fibers.

Unfortunately, for those of us living in Canada, the US, and Australia the amount of UVA protection offered by sunscreens is only given in relative terms. The UVA circle logo, for example, let’s you know that the UVA protection is at least 1/3rd of the SPF protection of the sunscreen, but it’s not as informative as a UVA protection factor (UVAPF) or persistent pigmentation darkening (PPD) number. While the PA system used in some Asian countries is based on a PPD number, the data is compressed into categories.

My personal thought is that the UVA protection should be as close to the SPF protection as possible. These are the sunscreens that I personally recommend; based on UVA protection, how they feel and wear on the skin, and affordability. While there are many great sunscreens out there, many of them are too expensive for me and I end up “rationing” them – which is a no-no when it comes to sunscreen application.

Bioderma Photoderm MAX Spray SPF 50+ with UVAPF 33 is a large sized and affordable sunscreen with a moderately high UVAPF. It is a lipid based formula (Dicaprylyl Carbonate) which spreads easily and is not greasy on the skin. I recommend the larger 400 mL size which comes with a snap lock which makes it easy to travel with. I use this on face and body.

It prices out to about 10 US cents per mL.

Sunscreen filters in bold:

Aqua/water/eau, Dicaprylyl Carbonate, Octocrylene, Methylene Bis-benzotriazolyl Tetramethylbutylphenol [Nano], Butyl Methoxydibenzoylmethane, Bis-ethylhexyloxyphenol Methoxyphenyl Triazine, Cyclopentasiloxane, Methylpropanediol, Ectoin, Mannitol, Xylitol, Rhamnose, Fructooligosaccharides, Laminaria Ochroleuca Extract, Decyl Glucoside, C20-22 Alkyl Phosphate, C20-22 Alcohols, Xanthan Gum, Propylene Glycol, Citric Acid, Caprylic/capric Triglyceride, Sodium Hydroxide, Microcrystalline Cellulose, Pentylene Glycol, 1,2-Hexanediol, Caprylyl Glycol, Cellulose Gum, Disodium EDTA.

Ombrelle Ultra Light Advanced Weightless Body Lotion SPF 50 is another affordable sunscreen I recommend. Canada’s Ombrelle was acquired by L’Oreal which is why this product contains Mexoryl sunscreens, which are patented and used exclusively by L’Oreal companies. Because of regulations, the UVAPF or PPD is not able to be listed, but this does have the UVA circle logo. It contains 2% Mexoryl SX which is the stronger UVA absorber compared to Mexoryl XL. It is lightweight, dries quickly, affordable, and easily accessible for Canadians. While it is marketed as a body sunscreen, I use it on my face. It’s much lighter in texture compared to Ombrelle’s other sunscreens marketed for the face.

It prices out to about 12 US cents per mL.

Sunscreen filters in bold

Homosalate: 10%, Oxybenzone: 6%, Octisalate: 5%, Octocrylene: 5%, Avobenzone: 3%, Ecamsul (Mexoryl® SX): 2%. Others/Autres: Aqua, Cyclopentasiloxane, Alcohol Denat., Cyclohexasiloxane, Styrene/Acrylatescopolymer, Silica, Dicaprylyl Ether, PEG-30 Dipolyhydroxystearate, Dimethicone, Triethanolamine, Glycerin, Nylon-12 Polymethylsilsesquioxane, Dicaprylyl Carbonate, Tocopherol, Dodecene, Phenoxyethanol, PEG-8 Laurate, Poly C10-30 Alkyl Acrylate, Poloxamer 407, Caprylyl Glycol, Disteardimonium Hectorite,Disodium EDTA, Lauryl PEG

Sheer Zinc Face Dry-Touch Sunscreen Broad Spectrum SPF 50 is a newer sunscreen and contains only Zinc Oxide as its sunscreen filter. Be warned, this has a very strong whitecast and a thick silicone texture which can pill. I find it best to apply this to small areas of the skin while blending thoroughly.

The reason why I recommend this sunscreen, despite its drawbacks, is based on a presentation that Johnson & Johnson gave at the 2017 American Academy of Dermatology’s Annual meeting showing that their 21.6% Zinc Oxide sunscreen had a UVAPF of 30. Other inorganic sunscreens I’ve seen have only been able to reach a UVAPF of about 18-25.

While the Neutrogena Sheer Zinc was not explicitly named, the launch time and Zinc Oxide content of 21.6% suggests to me that this is the product described.

They compared its absorption spectrum, in vitro, with other common inorganic sunscreens and were able to show that it absorbed more UVA in comparison

I must say again how strong the white cast is, hopefully in the future they release tinted versions!

Based on the above chart it’s likely that the tinted Elta MD SPF 41 with 9.0% Zinc Oxide and 7.0% Titanium Dioxide has a UVAPF of around 28, I’ve not personally tried the product, but I do know it is popular. It prices out to about 35 US cents per mL.

The Neutrogena Sheer Zinc prices out to about 15 US Cents per mL.

Sunscreen filters are in bold

Zinc Oxide 21.6%. Others: Water, C12-15 Alkyl Benzoate, Styrene/acrylates Copolymer, Octyldodecyl Citrate Crosspolymer, Phenyl Trimethicone, Cetyl PEG/PPG-10/1 Dimethicone, Dimethicone, Polyhydroxystearic Acid, Glycerin, Ethyl Methicone, Cetyl Dimethicone, Silica, Chrysanthemum Parthenium (Feverfew) Flower/leaf/stem Juice, Glyceryl Behenate, Phenethyl Alcohol, Caprylyl Glycol, Cetyl Dimethicone/bis-vinyldimethicone Crosspolymer, Acrylates/dimethicone Copolymer, Sodium Chloride, Phenoxyethanol, Chlorphenesin.

J.R.S. Gordon, J.C. Brieva, Unilateral Dermatoheliosis, The New England Journal of Medicine (2012), DOI: 10.1056/NEJMicm1104059

Visualizing how a daily sunscreen can protect the skin from UV damage

Optical coherence tomography and reflectance confocal microscopy can be used to non-invasively to visualize deep into the skin. Using these techniques we can actually see changes in the structure of the skin and its cells.

This group of researchers with funding from La Roche Posay used the imaging techniques to compare the effect of UVB exposure on skin protected with a high SPF and UVAPF sunscreen and skin that wasn’t protected.

What they found was that doses of UVB that caused long-lasting erythema (redness) caused morphological changes in the skin. Changes observed were spongiosis (abnormal accumulation of fluid), microvesicles, sunburn cells, and blood vessel dilation. None of these were observed in skin that was protected by the sunscreen.

A minimal erythemal dose or MED is the amount of UV energy that causes long-lasting redness in the skin. Just 1 MED was enough to cause morphological changes and 2 caused significantly more. This also relates to SPF. An SPF of 2 would provide enough protection to protect an average population against 2 MEDs.

If reducing your risk of developing skin cancers and preventing photoaging are a goal of yours – this is a great reminder and justification to wear your sunscreen daily!

Antonio Gomes-Neto, Paula Aguilera, Leonor Prieto, Sophie Seité, Dominique Moyal, Cristina Carrera, Josep Malvehy, Susana Puig, Efficacy of a Daily Protective Moisturizer with High UVB and UVA Photoprotection in Decreasing Ultraviolet Damage: Evaluation by Reflectance Confocal Microscopy, Acta Dermato-Venereologica (2018), DOI: 10.2340/00015555-2736

What’s causing sunscreen to stain clothing?

Yellow stains on your clothing? Your sunscreen might be a culprit!

A group of researchers tested 32 commercial sunscreens for their ability to stain white and black 100% cotton.

Of the tested sunscreens; Alba Botanica Hawaiian SPF 50 Spray, L’Oreal Invisible Protect SPF 50, Solbar Thirty, and Aveeno Protect and Hydrate SPF 50 were among the most staining sunscreens.

The least staining sunscreens were; Cerave Baby, Solbar Zinc 38, Cerave Face SPF50, and Babyganics Mineral Based SPF 50

Using statistical analysis to group the sunscreens by sunscreen ingredients they created four distinct groups. Based on these groupings they tested 8 sunscreen ingredients; Avobenzone, Homosalate, Octinoxate, Octisalate, Octocrylene, Oxybenzone, Titanium Dioxide, and Zinc Oxide.

For white fabric; Avobenzone was a strong yellow stainer and so was Oxybenzone to a lesser extent. Titanium Dioxide and Zinc Oxide both left faint white stains.

For dark blue fabric; Avobenzone and Oxybenzone both left faint white staining, but Titanium Dioxide and Zinc Oxide left strong white stains.

The sunscreen ingredients were applied directly to the fabric, whereas in real-life it’s likely transferred to skin by friction and smearing throughout the day

A sunscreen that stains is by no means a reflection of its ability to protect your skin from UV. If reducing extrinsic photoaging is a goal, it’s important to use a sunscreen frequently. Often people are discouraged from using sunscreens because of the texture, scent, and in some cases staining of their clothes.

If staining is an issue I’ve had good luck with soaking it with 99% isopropyl alcohol and then a soak in sodium percarbonate (Oxiclean) or hydrogen peroxide.

Cornell also has a great stain guide for a myriad of stains.

Ginnetti M, Buhnerkempe M, Wilson M, The staining of clothing by
sunscreens: a pilot study, Journal of the American Academy of Dermatology (2018), doi: 10.1016/j.jaad.2018.02.022