22 June 2022
One of the dermatological trends that has caught on in recent years is sunscreen becoming a staple in the skincare routine formost. UV rays from the sun is one of the biggest extrinsic cause of aging aand a risk factor for skin cancer. Celebrities like Hugh Jackman and Caitlyn Jenner are now advocating the diligent use of sunscreen following their skin cancer surgeries.
Hugh Jackman shares his journey with skin cancer and advice to wear sunscreen on his Instagram
Caitlyn Jenner was confirmed to have basal cell carcinoma, just like Hugh Jackman. Basal cell carcinoma is a type of skin cancer that can be caused by unprotected sun exposure.
A basic guide to choosing a sunscreen and the differences between a physical and chemical sunscreen. Credit:the American Academy of Dermatology
I find that most of my patients have a very rudimentary understanding of sunscreen: mostly to choose broad spectrum one, a high SPF value and to reapply every 2 hours. This blogpost will go beyond these basics and capture the important things to look out for when choosing sunscreen. I will not be covering the basics of sunscreen chemistry i.e. physical vs chemical filters (or more accurately, inorganic vs inorganic sunscreens filters because there is enough information online on that. Instead this post aims to add depth to what is already rehashed so many times; essentially: the latest trends in the field of sunscreen and some of the FAQ about sunscreen and sunblocks I get from my patients.
Types of filters and the coverage against UVA and UVB that each filter provides. As you can see, there are only 2 types of physical sunscreens- zinc oxide and titanium dioxide and the coverage of physical sunscreens are superior to most of the chemical sunscreens.
There is emerging data to show that visible light (more specifically, high energy visible light, HEVL) and infrared light emitted from our electronic devices including our smart phones and laptops can cause free radical formation and signs of aging in the skin1,2 What makes visible light and infrared light worrying is that these forms of are energy seem innocuous- they do not cause obvious signs of exposure the way sunrays cause sunburns on our skin. None of the physical or chemical sunscreens are able to provide protection against HEVL and infrared light because their wavelengths do not fall within the spectrum covered by the physical or chemical sunscreens.
How do HEVL and infrared damage our skin? There are 3 main postulated mechanisms:
1. Through activation of an enzyme called matrix metalloproteinase (MMP-1) which breaks down collagen in the dermis of the skin, causing wrinkles and sagging in the skin3.
2. The generation of free radicals or reactive oxygen species (ROS), which cause damage to cell DNA, proteins and other cell structures in the skin; similar to UV rays. ROS generated by HEVL and infrared light had a propensity to concentrate themselves in the mitochondria of cells4.
3. Pigmentation formation; independent of UV rays- but mainly for people who have darker skin (i.e. Fitzpatrick 4 and above) 5.
What is the relevance for us and how do we protect ourselves from the harmful effects of HEVL light and infrared? Well, logically, the first is to look out for sunscreens with filters against HEVL and infrared light. However, to date, there is no knownfilter that blocks out infrared and HEVL rays. There are a few reports of ingredients such such iron oxide6 and lutein that may hold promise; but until we have more scientific data, the jury is still out there. So for the sunscreens that claim to filter out blue light, HEVL and infrared light with plant extracts- the devil is in the details. Most of the scientific data so far shows that these plant extracts can help to reduce the level of MMP-1 and perhaps some of the ROS but they do not function as a true block out HEVL and infrared rays.
That said, your best bet would be to use a sunscreen that provides adequate broad spectrum coverage against UVA and UVB rays. And fret not, you do not have to limit your screen time; so please feel free to finish reading this post. The studies that have shown the damage that visible light and infrared rays do to our skin so far has been limited to in vitro studies (i.e. petri dishes in the lab) for 1) and 2). Also, for the studies that showed these harmful effects on the skin- the irradiance (think of it as “strength” and “exposure”) far outstripped (at a whooping 1952 hours) our daily exposure of HEVL and infrared; even for most of us who spend 6-9 hours on our smartphones and computers.
Second, add a topical antioxidant to up your protection against the free radicals generated by HEVL and infrared light. But take note, it’s not any antioxidant that will work. The combination of vitamin C with vitamin E and Ferulic has been shown in one human study has been shown to reduce the levels on MMP-1 following exposure to infrared light. The presence of ROS was not measured by this same study because ROS formation is not specific to HEVL or infrared light7. You might find this combination of antioxidants familiar because it is a personal favourite that I like to recommend to my patients. More about this in my blogpost, All About Topical Vitamin C.
Update: There is some data that suggests that iron oxide can absorb visible light15 (including blue light) and lighten pigmentation16. However, there is no consensus about the required dosage etc about iron oxide for the protection against blue light. You can find iron oxide in some sunscreens and makeup products like foundations. Which sunscreens contain iron oxide? My Sunscreen Reviews will share this with you.
How do you tell the amount of coverage against UVA and UVB rays of your sunscreen? The SPF value is an indicator of your protection against UVB rays and the PA value is an indicator of protection against UVA rays.
SPF protection stands for Sun Protection Factor and the value indicates the amount of protection against UVB rays (yes, not UVA rays). The SPF value is obtained by measuring the time it would take UV rays to turn your skin red when using the sunscreen product versus the time it would take if you were not using the product. In other words, for sunscreen with SPF 30, it would take 30 times longer for your skin to turn red when using the sunscreen than it would if you did not wear sunscreen.
So logically, the higher the SPF value, the better your protection right?
That is true, until we reach a point of diminishing returns.
Take a look at this graph from the US FDA, which measures the percentage of UV rays protection against the SPF value.
As the SPF value increases, so does the percentage of UV protection. However, this increase continues until about the SPF 30 mark, where there is 97% protection against UV rays. As the SPF value increases to SPF 50, there is only additional 1% protection, bringing the UV protection to 98%. This is why the US FDA recommends using sunscreen with SPF 30 or higher.
The caveat to enjoying the full UV protection as projected by the SPF value is that you have to apply a sunscreen thickness of 2mg/cm2. This is the recommended application thickness to reproduce the results of SPF testing.
As recommended by the American Academy of Dermatology, most adults require a shot glass worth of sunscreen for adequate sunscreen coverage for their whole bodies.
In reality, most of us do not apply a sufficient amount and thickness of sunscreen to enjoy the full SPF benefits of our sunscreens. Studies have shown that for most of us, we only apply 0.7-1.27 mg/cm2 of sunscreen- far below the recommended 2mg/cm2 guideline8,9.
What is the implication for us then? Sunscreen application thickness is related to the UV protection so this means that with an insufficient amount of sunscreen applied, the UV sunprotection is less than expected.
How much lesser is still not clear- there are studies that suggest an exponential relationship between sunscreen application thickness and SPF10,11. The consequence of an exponential relationship (hello secondary school mathematics) is that if a sunscreen with SPF 30 is applied insufficiently with half the recommended application thickness that the SPF value is reduced by the square root to… SPF 5.5. Shocking isn’t it?
In order to compensate for insufficient sunscreen application, choosing a sunscreen with higher SPF and frequent reapplication can help. I personally use a sunscreen with SPF 50, simply because sunscreens with higher SPF feel too cakey on the skin for me.
Another trend that is currently very popular is the use of oral sunscreens. There is a popular misconception that oral sunscreens can replace the use of topical sunscreens.
Let us first start with the basics of oral sunscreens: what are they really and how do they work?
Oral sunscreens are a type of dietary supplement that claim to provide protection against the sun. Unfortunately, some these claims have been found to be misleading the public and the US FDA has released a press statement this year calling out the companies and products that have been misleading the public12.
FDA’s warning against oral sunscreen, as covered by TIME magazine
Of all the ingredients that claim to provide sunprotection, Polypodium Leucotomos, an extract from fern plants native to South America, has the strongest research. This extract is also known as Fernblock and is a mix of antioxidant compounds. How Fernblock works is not entirely clear- possible explanations include neutralisation of free radicals and reduction of inflammation based on in vitro and animal studies13,14 . In other words, Fernblock does not block out UV rays from the sun the way a topical sunscreen does.
So far there are no studies that demonstrate that oral sunscreens that are as effective as topical sunscreens in protecting from UV rays. To quote the US FDA, “There’s no pill or capsule that can replace your topical sunscreen12.”
Earlier this year, I was invited to test out a sunscreen body wash called Klenskin shower on sunscreen that is now stocked in some clinics in Singapore. The pitch was very enticing- the first of its kind shower on sunscreen that provides sunprotection to people who did not like to or want to wear sunscreen. It sounded like an interesting idea- a sunscreen soap/body wash that could overcome some of the problems of a topical sunscreen- the white cast, sticky feeling and perhaps, people who forget to wear their sunscreen.
So I gamely tried it, but of course paired it with my topical sunscreen. No smell, no negative reaction but it is difficult to give a review with samples that were enough for 3 showers. Nevertheless, let us look at some of the claims and data about Klenskin and sunscreen body washes.
According to their website, Klenskin’s claims to provide broad spectrum SPF 30 using its “quantasphere encapsulated sunscreen”. The active ingredients are a combination of chemical or organic sunscreens: Avobenzone, Octocrylene and Octinoxate. The encapsulated sunscreen is apparently positively charged and binds to negatively charged skin and hair and so the sunscreen remains on the skin after rinsing and drying.
A look at the trial sponsored by Klenskin’s manufacturer shows that there seems to be SPF protection after rinsing off Klenskin’s shower on sunscreen for their very small study of 10 subjects. There are no other studies or data available at this time of writing that support the the efficacy or use of Klenskin. Questions that need to be answered include how long Klenskin’s shower on sunscreen remains on the skin; whether it can be used as a standalone substitute for sunscreen…etc). Until this data comes along, it is probably better to stick to a topical sunscreen and use Klenskin’s shower on sunscreen as a supplement.
I hope that this blogpost gives you a more in-depth understanding of sunscreen and the trends surrounding sunscreen. A lot of the claims about sunscreen sound promising but need more data to support their claims. In summary, I leave you with my sunscreen tips and stay tuned for an upcoming post where I review sunscreens I have tried and share with you my favourites!
Use a broad spectrum sunscreen for protection against UVA and UVB rays
The higher the SPF and PA protection; the better.
Pair your sunscreen with antioxidants to increase your protection against sun damage- my recommendation is the tried and tested combination of vitamin C, vitamin E and Ferulic.
Do not worry too much about skin damage from light and electronic devices- the data so far shows damage with excessive exposure. Focus on protecting your skin from UVA and UVB damage. Besides, there is still no known filter for visible light and blue light.
Use oral or wash off sunscreens as an add on to your routine of topical sunscreen use and not as a replacement.REFERENCES 1. Light—instead of UV protection: new requirements for skin cancer prevention. Zastrow and Lademann J.Anticancer Res. 2016;36(3):1389–93 2. Impact of long-wavelength UVA and visible light on melanocompetent skin. Mahmoud et al. J Investig Dermatol. 2010;130(8):2092–7 3. Infrared-A radiation-induced matrix metaloproteinase 1 expression is mediated through extracellular signal regulated kinase 1/2 activation in human dermalfibroblasts. Schieke et al. J Invest Dermatol 2002; 119: 1323–1329. 4. Infrared radiation-induced matrix metalloproteinase in human skin: implications for protection. Schroeder et al. J Invest Dermatol 2008; 128: 2491–2497 5. Impact of long-wavelength UVA and visible light on melanocompetent skin. Mahmoud et al. J Invest Dermatol 2010; 130: 2092–2097 6. New data on hyperpigmentation disorders. Schalka. JEADV 2017. Suppl 5; 18-21. 7. Topical L-ascorbic acid: Percutaneous absorption studies. Pinnell et al. Dermatol Surg 2001; 27: 137–142. 8. Application of sunscreen preparations: a need to change the regulations. Reich et al. Photodermatol Photoimmunol Photomed. 2009 Oct;25(5):242-4 9. Relationship between sun-protection factor and application thickness in high-performance sunscreen: double application of sunscreen is recommended. Teramura et al. Clin Exp Dermatol. 2012 Dec;37(8):904-8 10. The relation between sun protection factor and amount of suncreen applied in vivo. Faurschou ans Wulf. Br J Dermatol. 2007 Apr;156(4):716-9. 11. The relation between the amount of sunscreen applied and the sun protection factor in Asian skin. Kim et al. J Am Acad Dermatol. 2010 Feb;62(2):218-22. 12. https://www.fda.gov/newsevents/newsroom/pressannouncements/ucm608499.htm 13.Inhibition of ultraviolet-induced formation of reactive oxygen species, lipid peroxidation, erythema and skin photosensitization by Polypodium leucotomos. Gonzalez and Pathak. Photodermatol Photoimmunol Photomed. (1996) 12:45–56. 14. Polypodium leucotomos extract inhibits glutathione oxidation and prevents Langerhans cell depletion induced by UVB/UVA radiation in a hairless rat model. Mulero et al. Exp Dermatol. (2008) 17:653–8. 15. Efficiency of opaque photoprotective agents in the visible light range. Kaye et al. Arch Dermatol. 1991 Mar;127(3):351-5. 16. A method to assess the protective efficacy of sunscreens against visible light‐induced pigmentation. Duteil et al. Photodermatol Photoimmunol Photomed. 2017 Sep;33(5):260-266