Should I Wear Sunscreen Indoors?

It is becoming more widely known and accepted that daily sunscreen use is the number one skincare tip for younger looking skin. Dermatologists have known this for decades, but there is a surprising amount of resistance from sun worshipers. Many people still believe that a sun tan makes you look healthier and it’s hard to break this mind-set. These sun-kissed people may think that the sunscreen enthusiasts that wonder “should I wear sunscreen indoors?” are taking it too far.

However, what they don’t realise is that most windows do not block all UV radiation.

So yes, you should wear sunscreen indoors and here is why…

Should I Wear Sunscreen Indoors?

If you are reading this article, then I’m going to go ahead and assume that you know just how important sunscreen is for skin health and how it can keep your skin looking younger. The key points being that sunscreen:

• Protects skin from skin cancer by preventing UV rays from penetrating the skin and causing DNA damage.
• Prevents UV radiation breaking down collagen and elastin in the skin and making skin appear more wrinkled and ‘saggy’.

Here’s a quick recap of the different types of solar radiation and UV radiation:

Solar Radiation

Solar radiation is the radiation produced by the sun. The solar radiation that is able to reach our skin is mainly made up of:

• 53% infrared radiation (780-5000nm wavelength)
• 39-44% visible light (400-780nm wavelength)
• 3-7% UV radiation (290-400nm wavelength) ^[1]

UV Radiation

UV radiation is further broken down into UVA (340-400nm), UVB (290-320nm), and UVC (200-290nm). (UVA can be even further broken down into UVA1 340-400nmand UVA2 320-340nm) ^[2].

UVC rays are entirely absorbed by the earths atmosphere and unable to reach our skin, unlike UVA and UVB rays. So what’s so damaging about UVA and UVB rays?

A general rule of thumb is that UVA rays cause Agingand UVB rays cause Burning.Of course, it’s not quite as simple as that, so here is a little more information:

• UVA– These rays penetrate deeper into the deeper layer of the skin (the dermis) where they can cause DNA damage and cell mutation. They also break down collagen and elastin that makes the skin appear more wrinkled over time. UVA rays account for 95% of UV radiation, are relatively constant all year round, and can penetrate through glass. The biggest issue with UVA rays is that the damage caused is accumulative and invisible to the naked eye.

• UVB – These rays account for less than 5% of UV radiation and are stronger in the summer months (i.e. hot and sunny weather). Due to their shorter wavelength, UVB rays are only able to penetrate the epidermis where they can cause DNA damage and cell mutation. This damage is noticeable almost instantly as sunburn (caused by an inflammatory reaction to the damage caused) or a suntan. UVB rays are also almost entirely absorbed by glass ^[2].

So, what does this all mean? Why should I wear sunscreen indoors?

Why You Should Wear Sunscreen Indoors

As mentioned, standard glass windows are only able to block (by absorbing) UVB rays while UVA rays are able to pass freely through (are not absorbed by glass).

This means that if you are indoors you are still exposed to harmful UVA rays if there are windows nearby. This is particularly evident from studies that have looked at facial aging asymmetry in individuals whose jobs or activities expose them to sunlight through a nearby window (e.g. having their office desk next to a window) ^[3][4][5].

For example, one study found that people had more wrinkles, deeper crow’s feet, lower skin elasticity, and a duller and drier complexion on the side of their face that was exposed to light through a nearby window ^[3].

Another study found that the incidences of skin cancers are more prevalent on the drivers-side of the face and body. This, of course, is the side of the body that would be exposed to light through the driver’s side window ^[4].

One of the best documented examples of facial aging asymmetry due to light exposure through widows, however, was that of a long-distance truck driver after 28 years on the job. Again, the left side of his face (the side of his face that was exposed to light through the driver’s side window) had noticeably more sun damage than the right side of his face ^[5].

Check out the sunscreens with the highest UVA protection here!

Gordon, J. & Brieva, J. (2012). ‘Unilateral Dermatoheliosis’, New England Journal of Medicine, 366. 

This visual paints a pretty shocking truth about just how much UV damage can occur through standard windows. But what about visible light and infrared radiation?

Indoor Visible Light and Infrared Radiation

The DNA damaged caused by UV radiation is due to the production of free radicals (ROS). However, UV radiation isn’t the only form of solar radiation to cause the production of free radicals. Both visible light and infrared radiation have been suggested to cause free radical damage and contribute to skin aging.

One study identified that, while UV radiation accounted for the majority of free radical production in the substratum corneum (67%), visible light still accounted for over a third (33%) ^[6]. As you may have guessed, visible light is freely able to pass through glass. In fact, visible light is the light that we can see with the naked eye, so if its not dark then there is visible light present.

Of note is the arbitrary cut off between UVA radiation and visible light. Apparently, 400nm is where UVA radiation ends and visible light begins. So why, then, is a wavelength of 399nm harmful but a wavelength of 401nm isn’t?

The answer is that it isn’t less harmful –  enter blue light. Blue light is often referred to as high energy visible (HEV) light as blue light photons have a higher energy than other wavelengths in the visible spectrum. Some research has suggested that excessive blue light exposure can lead to cell abnormalities and cell death ^[7].

Guess where HEV light is also present? – that’s right! HEV light is present in computer and mobile phone screens. As many people work upwards of 40 hours-a-week in front of a computer screen in an office full of big windows, more skin damage occurs indoors than you may think!

So what kind of sunscreen should I wear indoors in order to protect my skin as much as possible?

How To Protect Your Skin From UV Damage & Visible Light Damage Indoors

Research suggests that zinc oxide and titanium dioxide containing sunscreens (a.k.a. mineral/physical/inorganic sunscreens) are far better at protecting the skin from longer UVA rays and visible light than conventional chemical sunscreens ^[8]. This is due to the fact that they reflect and scatter light as opposed to absorbing it. However, they do not provide adequate visible light protection.

The addition of iron oxide into mineral sunscreens has demonstrated the ability to broaden photoprotection into the longer UVA and visible light spectrums ^[9]. However, the jury is still out on just how much extra protection it offers. For example, some research suggests that it is only effective at blocking visible light in the blue range ^[9], whereas other research has suggested that iron oxide is effective at absorbing all wavelengths of visible light ^[8].

When it comes to free radical damage, even with the correct application, sunscreens can only block 55% of the free radicals produced by UV exposure ^[10]. So how can we boost our protection from free radical damage? That’s where antioxidants come in!

Anti-oxidants can neutralise the free radicals produced by UV radiation and visible light, as if they were “mopping-up the damage”. They can also reduce the number of free radicals produced in the first place.

For example, one study compared a pre-treatment of either broad-spectrum sunscreen with added antioxidants, the same sunscreen without the antioxidants, and the antioxidants alone before exposing skin to visible light. As expected, exposure to visible light caused a significant increase in free radicals (specifically ROS). Pre-treatment with sunscreen alone had no effect on reducing the damage from visible light. However, pre-treatment with a sunscreen containing added antioxidants resulted in a 78% reduction in ROS ^[11].

It was also noted that antioxidants alone caused a similar reduction in ROS, although the exact statistic was not discussed in the research paper.

Summary – Should I Wear Sunscreen Indoors?

Yes. You should absolutely wear sunscreen indoors, especially if your place of work has a lot of windows and/or computer screens and other forms of HEV.

But, sunscreen alone may not be enough. Here’s a low-down on the different ways you can protect your skin from the types of solar radiation you may be exposed to indoors:

Some protection: Antioxidants

Adequate Protection: Sunscreen

Good Protection: Mineral Sunscreen

Excellent Protection: Mineral Sunscreen with Antioxidants

Super-Duper Protection: Mineral Sunscreen with Iron Oxide AND Antioxidants

Over-The-Top Protection: Balaclava, Sunglasses, and a Sombrero

References

1. Frederick, J., Snell, H. & Haywood, E. (1989) ‘Solar ultraviolet radiation at the earth’s surface’, Photochem Photobiol, 50, pp. 443–450. https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1751-1097.1989.tb05548.x
2. Palm, M. & O’Donoghue, M. (2007). ‘Update on photoprotection’, Dermatologic Therapy, 20(5), 360-376. Available at: https://onlinelibrary.wiley.com/doi/full/10.1111/j.1529-8019.2007.00150.x
3. Mac-Mary, S., Sainthillier, JM., Jeudy, A., Sladen, C., Williams, C., Bell, M., & Humbert, P. (2010). ‘Assessment of cumulative exposure to UVA through the study of asymmetrical facial skin aging’. Clinical Interventions in Aging, 5, 277-284. Available at:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2946854/
4. Butler, ST., & Fosko, SW.(2010)‘Increased prevalence of left-sided skin cancers.’ Journal of the American Academy of Dermatology, 63(6), 1006-10. Available at:https://www.ncbi.nlm.nih.gov/pubmed/20226568
5. Gordon, J. & Brieva, J. (2012). ‘Unilateral Dermatoheliosis’, New England Journal of Medicine, 366, Available at: https://www.nejm.org/doi/full/10.1056/NEJMicm1104059
6. Haywood, R. (2006) Relevance of sunscreen application method, visible light and sunlight intensity to free-radical protection: A study of ex vivo human skin. Photochem. Photobiol. 82, 1123– 1131. Available at: https://www.ncbi.nlm.nih.gov/pubmed/17205635
7. Bennet, D., Viswanath, B., Kim, S. & An, J. (2017). ‘An ultra-sensitive biophysical risk assessment on light effect on skin cells’, Oncotarget, 8(29), 47861-4785. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5564611/
8. Kaye, E., Levin, J., Blank, I. et al. (1991). ‘Efficiency of opaque photoprotective agents in the visible light range’, Ach Dermatol, 127(3), 351-355. Available at: https://jamanetwork.com/journals/jamadermatology/article-abstract/552806
9. Castanedo-Cazares, J., Hernandez-Blanco, D., Carlos-Ortega, B., Fuentes-Ahumada, C. & Torres-Alvarez, B. (2013). ‘Near visible light and UV photoprotection in the treatment of melasma: a double-blind randomized trial’, Photodermatology, Photoimmunology & Photomedicne, 30(1), 35-42. Available at: https://onlinelibrary.wiley.com/doi/abs/10.1111/phpp.12086
10. Haywood, R., Wardman, P., Sanders, R. & Linge, C. (2003). ‘Sunscreens inadequately protect against ultraviolet-A-induced free radicals in skin: implications for skin aging and melanoma?’, J Invest Dermatol, 121(4), 862-868. Available at: https://www.ncbi.nlm.nih.gov/pubmed/14632206
11. Liebel, F., Kaur, S., Ruvolo, E., Kollias, N. & Southall, M. (2012). ‘Irradiation of skin with visible light induced reactive oxygen species and matrix degrading enzymes’, J Invest Dermatol., 132(7), pp. 1901-1907. Available at: https://www.sciencedirect.com/science/article/pii/S0022202X15358292