Sun protection guide

Sun damage is the main cause of visible skin aging. It also causes pigmentation issues, increases scarring from wounds and can lead to larger pores as skin ages. This is why sunscreen is the most important and effective component of any skincare regimen, either it is aimed at anti-aging, acne, or pigmentation. It is needed for any skin tone, including the darkest.

Sunscreen also prevents skin cancer. For both health and cosmetic goals, your sunscreen needs to be broad-spectrum (protect from both UVA and UVB rays), and have an SPF factor of 30 or more. Sunscreen is needed every time you go outside or sit next to a window without built-in UV filters, even if the weather is cloudy. Sun damage accumulates during our lifetime. This is why the earlier you start wearing sunscreen daily, the younger and better your skin will look later in life. Protecting kids’ skin from sun damage is important for their later skin health (and looks) too.

How does sunlight lead to skin aging?

How exactly can something as nice, warm and mood-boosting as sunlight cause the harm? What does UV radiation actually do to our skin that causes wrinkles and elasticity loss?

The main mechanism of damage is the following. UV light activates cell receptors in the epidermis (upper) and dermis (deeper layer) of our skin. This activation happens within 15 min of sun exposure and lasts for at least 2 hours after it.

The activated receptors start accepting distress signals from outside of the cells. It happens within 30 min of sun exposure and lasts for full 24 hours. The signals activate enzymes within the cells, and the enzymes, in turn, start synthesis of special proteins with the function of "cleaning up" a site of skin wound. The "cleaning up" involves destruction of collagen fibers in the skin.

A single UV exposure causes a strong rise in production of the collagen-killing proteins, and their concentration returns to normal only after 48-72 hours after sun exposure.

Skin cells produce new collagen after the old fibers get destroyed. Unfortunately, this repair is not perfect. The "new" collagen matrix is less robust that the "old" one, and this deterioration progresses every time with new sun exposure. Dermatologists call this process "solar scarring". Over time, exposure to UV leads to accumulation of solar scars, and we get photoaged, wrinkled skin.

Sunlight & skin: UVA and UVB explained

Sun radiates different types of light. Some of it falls into the so-called ultraviolet range (UV light). When you hear the terms "sun protection" and "sunscreen", what is usually meant is protection from the UV light.

The effect of light on the skin depends on the length of its wave. The shorter the wave, the more energy it has, but also, the more "shallow" it is in terms of how deep it can penetrate into our skin. The longer the wave, the less powerful it is in terms of energy, but the deeper it can penetrate into the skin.

Depending on the wavelength, we differentiate ultraviolet light type A (UVA), ultraviolet light type B (UVB), and ultraviolet light type C (UVC). UVC rays are the shortest, most powerful, and least penetrating, while the UVA rays are the least powerful, but the most penetrating among the three types. Luckily, the ozone layer in the atmosphere absorbs the UVC rays so they don't reach the Earth surface and don't get a chance to harm our skin.

UVB and UVA rays, however, make it through. UVB rays, as their wavelength is short and energy is high, cause an immediate damage to our skin causing a sunburn and a direct DNA damage in our epidermis (the top layer of our skin). This damage can lead to skin cancers and aging.

UVA rays are longer and less powerful, so they do not cause an immediate visible damage. You don't get a sunburn from the UVA rays. However, because their waves are longer, they can penetrate deeper into the skin, damaging the dermis - the skin layer with collagen and elastin fibers. This is why UVA rays are sometimes called the "UV-Aging" (as opposed to the UV-Burning) rays. Even though the UVA rays do not cause a direct damage to the cell's DNA, they harm it indirectly by producing free radicals that then, in turn, lead to skin aging (wrinkles, age spots, elasticity loss), inflammation and DNA damage. By doing so, UVA rays increase the risk of skin cancer.

This means that our skin needs protection from both the UVB and UVA light. It is important to remember that not all sunscreens can protect from both the UVB and UVA light. In fact, until recently, the filters used in sunscreens offered a meaningful protection against the UVB rays only. Luckily, in the recent decades, scientists have been working hard on developing new sunscreen filters that would offer a broad spectrum protection (meaning protection against both the UVB and UVA rays). These new sunscreen filters are widely used in sunscreens today in most parts of the world (with the exception of the US, unfortunately: most of these new generation filters are not approved by the FDA yet and cannot be incorporated in the sunscreens sold in the country).

Sunscreen filters for UVB rays

UVB rays are known to cause sunburn, skin cancer, and accelerate skin aging. UVB rays are defined based on the length of their wave. UVB light has a wavelength between 290 and 320 nanometers. This is shorter than UVA. This is why UVB rays do not penetrate human skin as deep as the UVA light. At the same time, UVB light has more energy in it, meaning that it can cause a more direct damage to the skin cells (and their DNA more specifically).

Some of the common UVB filters used in sunscreen include:

  • Titanium dioxide

  • Octocrylene

  • Homosalate

  • Octinoxate

  • Oxybenzone

  • Uvasorb HEB (not approved by the US FDA)

  • Uvinul T (not approved by the US FDA).

In addition to the UVB filters, broad spectrum filters offer good protection from both the UVB and UVA rays. Among them:

  • Mexoryl SX

  • Zinc oxide

  • Mexoryl XL (not approved by the US FDA)

  • Tinosorb M (not approved by the US FDA)

  • Tinosorb S (not approved by the US FDA)

Sunscreen filters for UVA rays

UVA rays cause premature skin aging with wrinkles, elasticity loss, and age spots. They can also trigger hyperpigmentation (for example, post-acne marks and melasma). UVA rays are responsible for the natural tanning of our skin (this is why the so called "healthy tan" always comes together with skin damage). UVA rays contribute to the development of skin cancers.

UVA light has a wavelength between 320 and 400 nanometers. Not all UVA sunscreen filters can cover this range in full, and this is why it is useful to split the UVA spectrum further into the UVA I (the longest UVA waves with the length of 340 to 400 nanometers) and UVA II (shorter UVA waves with the length of 320 to 340 nanometers). Most of the UV radiation we are exposed to falls within the UVA I range (long rays). At the same time, protection against the UVA I rays (the longer ones) is the most tricky to achieve. Because of that, in skincare, a sunscreen filter is defined as a UVA one in most cases only if it is able to protect against the long UVA waves (UVA I).

In general, all UVA waves are shorter than the UVB ones. This is why they are able to penetrate human skin deeper than the UVB light. At the same time, UVA light has less energy in it, meaning that it does not cause a direct damage to the skin cell DNA in the same way that the UVB rays do. Unfortunately, it is still causing the DNA damage, but through an indirect mechanism (it creates free radicals that then can cause chemical reactions that are harmful to the skin health).

UVA light reaches the surface of Earth even when the weather is cloudy. It can also penetrate through glass in windows.

Some of the popular UVA / broad spectrum filters used in sunscreen include (all of the ones listed below protect from the long, UVA I rays; broad spectrum filters protect both from the UVA and UVB light):

  • Zinc oxide

  • Mexoryl SX

  • Avobenzone

  • Mexoryl XL (not available in the US)

  • Tinosorb M (not available in the US)

  • Tinosorb S (not available in the US)

Mineral vs. organic sunscreen filters

There are two types of sunscreen filters in sunscreen based on their chemical nature. The first type is non-organic, or mineral filters. There are only two of those: Zinc Oxide and Titanium Dioxide. These filters are mineral, or non-organic because their molecules do not contain carbon atoms (you might recall from a high school chemistry class the distinction between “organic” and “non-organic” chemistry. Important note: it has nothing to do with “organic farming”). To make matters more confusing, the non-organic, or mineral sunscreens are sometimes called “physical” (for no good reason).

Mineral sunscreen filters almost never lead to skin irritation and can work even for the most sensitive & reactive skin. This is why mineral-only sunscreens are preferred for babies and children. They also don't sting the eyes. Another “plus” for the mineral filters is that they are stable (do not degrade quickly when exposed to sun). This makes it easier to formulate minimum-ingredient sunscreens with them: they do not require additional “stabilizers” and UV protection helpers in the formula.

Browse mineral-only sunscreens here.

Unfortunately, they have disadvantages too. Their cosmetic elegance (or lack of it) is a huge one. Mineral filters generally require quite a thick product texture to function properly, and more often than not, they leave a white to grey, chalky finish on the skin. This is often a no-go for darker skin tones. In recent years, formulators have been able to achieve way more elegant formulations using very finely milled and coated zinc oxide particles (microfine and nanoparticles). Based on the available research, these finely milled mineral filters are safe both in terms of the skin irritation potential and the general impact on the body.

The other challenge with the mineral filters is that they are not the strongest ones. 10% Zinc Oxide (nano), for example, on average, provides an SPF of about 5 (without additional sunscreen boosters). 10% of Titanium Dioxide provides an SPF of about 20, but 10% of titanium dioxide looks very, very white and not appealing. In addition, Titanium Dioxide cannot offer a sufficient protection from the UVA rays (the long ones, UVA I).

Overall, formulating a sunscreen with mineral filters only that is able to provide a sufficiently high protection from both UVB and UVA rays while being cosmetically acceptable for daily use is very difficult. Hence such products are a rare find, and typically provide an SPF around 30.

How about the organic, or "chemical" sunscreens? While there are only 2 non-organic sun filters, there are dozens of organic ones, which makes it difficult to speak about them as one group. Some of the early organic sunscreen filters (for example, Oxybenzone, Sulisobenzone, PABA) are frequent irritants, while others (for example, Tinosorb M and S, Homosolate) seem to have a low irritation risk. Some of the "chemical" filters are unstable (as in lose their effectiveness quickly when exposed to sun, for example, Avobenzone), while others are very stable (for example, most "new generation" filters like Mexoryls and Tinosorbs). The best UVA protectors are in the organic sunscreen group.

Overall, the rule of thumb is that the "new generation" filters are better on all fronts (broad spectrum protection, efficiency, and stability) compared to the early organic filters and, if formulated well, can rival the safety of mineral products.

Here is a catch though: unfortunately, most of the "new generation" organic sun filters are not available in the US because they are not approved by the FDA (while they have been safely used for decades in Europe and Asia).

Another point to keep in mind: some sunscreens are advertised as mineral, but still contain organic actives that function as UV filters. The common ingredient used this way is Butyloctyl Salicylate. It is not recognized as an official UV filters by sunscreen regulators, but it protects in the UVB range. There is nothing wrong with it (and it rarely causes sensitivity), but it is slightly dishonest to call a sunscreen with it "mineral".

New generation sunscreen filters

"New generation" sunscreen filters are compounds that were designed specifically for skin protection. Most of them were developed & tested in the 90s and 2000s. These filters are typically stable and provide reliable protection in their range. Sunscreens that include them usually perform better than products with older filters. Unfortunately, the US FDA is very slow in studying these new compounds. Even though they have been safely used in Europe and many other parts of the world, most of them are still not approved by the FDA. Products with these filters are still often available to the US consumers via international shipping or though other FDA loopholes.

The "new generation" filters include:

Browse sunscreens with new generation filters here.

Sunscreen filters to avoid for sensitive skin

The sunscreen ingredients below are the most common irritants in the UV filter category. It does not mean that they are necessarily irritating for your skin, but if you have an irritant reaction to a sunscreen, these are the first suspects:

The safest choice for very reactive skin and skin prone to eczema and other chronic skin conditions is a fragrance-free mineral sunscreen. They are also the best choice for babies. Browse good product options here.

Visible & infrared light

Compared to UVB and UVA rays, visible has the longest wavelength. It means that it has less energy, but can penetrate deeper into the skin. The visible light splits into colors, depending on the wavelength. The shortest visible lightwaves are blue. From all visible light, the blue light is the closest to UV radiation in terms of its effect on skin. This is why in skincare chatter, you often hear about blue light specifically instead of visible light in general. Red light has the longest wavelengths and the least energy from the visible spectrum. Infrared light is what comes after red on the light (radiation) spectrum. Its waves are longer than the red light (so even less energy but deeper penetration). We do not see infrared radiation but we feel it: it is warmth.

Visible and infrared light (heat) creates free radicals in skin, and in this way it can contribute to skin aging. These types of light also can trigger pigmentation in skin. At the same time, it is important to keep in mind that this damage is way, way smaller compared to the damage we get from the UVA and UVB. This is why the priority in skincare is the UVA & UVB protection. Only once you get this covered well, it makes sense to think about protection from the visible light and heat.

Protecting your skin from visible light is very difficult in practice. Only optically opaque materials can do it. This is why you can’t have a cream that would be not perceptible on your skin and at the same time protect from visible light. Heavy white zinc oxides pastes can protect from visible light. But you’d also look pretty white with those on. Tinosorb M sunscreen filter can also offer some protection in the visible spectrum, but, again it would come with a visible white layer. This is where tinted sunscreens and makeup come in: opaque foundations can protect from visible radiation. The protection is usually due to iron oxides that give a sunscreen or makeup a tint. The heavier / fuller coverage the tinted product is, the more protection against the visible light it can offer.

A lot of skincare products these days claim visible or blue light protection, but what they usually mean is some protection from free radicals generated by it, not protection from the light itself.

Also worth mentioning that the main source of blue and other visible light is the sun, and not device screens. Yes, it’s true that screens emit blue light, but the amount is neglectable compared to our daily exposure to visible light from the sun.

The bottom line: yes, it is true that the blue and all other types of visible light and infrared radiation (heat) can contribute to skin aging and pigmentation. But their effect is way smaller than that of the UV light. Protecting from visible light is also not always possible to fit into one’s lifestyle. If you are diligently protecting your skin from the UV rays, you are already making a huge difference for the health and beauty of your skin. By comparison, protection from the visible light is not such a huge deal (but wearing a tinted sunscreen or a foundation is a plus).

Positive effects of UV and other radiation on skin

Sun, different types of visible light and other types of radiation can have a therapeutic effect in skin. Skin biology is very complex, and things that impact biological processes in skin often have both a positive and negative effect. A qualified dermatologist can determine if the benefit of UV, light or other type of therapy outweighs the side effects in your particular case. The devices used in these types of treatment are engineered in a way to precisely omit only a certain wavelength. By comparison, the sun emits a wide range of radiation, and you don’t have control over what hits your skin. The treatments themselves are also very short and target a precise skin area. The risks of exposing your skin to UV, light and other forms of radiation without control and supervision almost certainly tramp any potential benefit.

UVB radiation kicks-off the synthesis of Vitamin D in our skin. Studies show that daily sunscreen use, however, does not lead to the Vitamin D deficiency.


Human Safety and Efficacy of Ultraviolet Filters and Sunscreen Products

UV Filters: Challenges and Prospects

Fisher, G. J., Talwar, H. S., Lin, J., & Voorhees, J. J. (1999). Molecular Mechanisms of Photoaging in Human Skin In Vivo and Their Prevention by All-Trans Retinoic Acid. Photochemistry and Photobiology, 69(2), 154–157. Fisher, G. J.

Talwar, H. S., Lin, J., & Voorhees, J. J. (1999). Molecular Mechanisms of Photoaging in Human Skin In Vivo and Their Prevention by All-Trans Retinoic Acid. Photochemistry and Photobiology, 69(2), 154–157. doi:10.1111/j.1751-1097.1999.tb03268.x

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Porcia B. Love, Roopal V. Kundu. Clinical Cases in Skin of Color

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Jackson-Richards D, Pandya AG. Dermatology Atlas for Skin of Color

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