How does sunscreen work?

There is so much more being said these days about sunscreens that answering the question "how does sunscreen work?" and how important it is to use sunscreen to avoid the ever increasing occurrence of skin cancer are of vital importance. The statistics are presented in a way that we can't really afford to ignore the warnings, especially if you are a skin type one with fair skin with blue eyes! So, this question, when answered and understood, will significantly help you to choose.

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The essential purpose of a sunscreen is to prevent us from being exposed to the sun's UV rays and incurring any DNA damage that can lead to the dreaded skin cancer. Although sunshine is hugely important to all living creatures on earth in one way or another, too much too quickly can be detrimental.

As you can see in the diagram below, the sun's rays consist of many different types. It is the Ultra Violet (UV) photons that sunscreens focus on preventing from damaging our skin. These UV photons are shorter in wavelength and higher in energy than visible light, and being outside the visible spectrum, we are not able to see them.

When these high-energy UV photons strike your skin, they generate free radicals, which unless controlled by your natural built-in defence systems, can ultimately damage your DNA, prematurely age your skin, and possibly result in skin cancer.


UVA and UVB rays

An understanding of the nature of these rays is essential for clear answers to the question 'how does sunscreen work?'. The UVB and UVA rays reach us on earth but the UVC rays are stopped at the ozone layer, (although the depletion of upper atmospheric ozone has people debating whether or not the UVC rays do actually reach us?).

The shorter wavelength UVB rays don't penetrate as deeply into our skin as the UVA rays, but are known to be the primary cause of sunburn. The longer wavelength UVA rays penetrate deeper into the layers of the skin, where they are known to be the ones responsible for the premature aging of the skin and immunologic problems. Both produce free radicals and through significant damage to the DNA, can ultimately cause skin cancer.

Sunscreen active ingredients

In answering the question of how does sunscreen work, there are just 2 main sunscreen active ingredient types to know:

  • Inorganic - also called natural, physical or mineral sunscreens. These consist of either Zinc Oxide or Titanium Dioxide
  • Organic - also called chemical sunscreens. These officially number anything from 17 - 25 depending on which country you are in. They include octyl methoxycinnamate (OMC), 4-methylbenzylidene camphor (4-MBC), avobenzone, oxybenzone, and homosalate amongst others

Both the inorganic and organic types protect against UVB rays (280- to 320-nm range). Both of the inorganic (natural) ingredients protect against both UVA and UVB rays (280 400 nm range).

A small number of the organic (chemical) ingredients also protect against a portion of the UVA ray range (320- to 400-nm).

Formulators often combine the inorganic and organic sunscreen ingredients for a synergistic effect. This is how it is possible to achieve very high SPF (sun protection factor) ratings. SPF being a measure of how effectively a sunscreen limits skin exposure to the UVB rays only.

SPF does not measure the protection provided against UVA radiation. Some sunscreens will say their products contain "broad-spectrum" protection, which means they provide protection against both UVA and UVB rays, but there is no indication of how much UVA protection is provided.

UVA certification methods are varied across the world, with no one single method having been identified as a global standard. However, it is important to find a sunscreen that does at least have some sort of certification for their UVA protection to make sure it is high enough.

Among the inorganic sunscreen ingredients, zinc oxide offers much better UVA protection than Titanium Dioxide.

The Future and 'how does sunscreen work?'

There is an interesting trend emerging whereby nature is teaching biologists how to beat back the sun and repair what damage it causes. Researchers are looking more and more towards nature for solutions to all sorts of things, including sunscreen ingredients and formulas. There is a science called Biomimicry that focuses on this and is evolving fast.

Some plants have natural defenses against the damaging rays of the sun and a few are cited below.


First is the mushroom coral, which secretes a mucus to protect it from the sun's UV rays when exposed.


Other studies, with surprising answers to the question 'how does sunscreen work?', suggest that most corals act as a sunscreen, absorbing UV light and limiting the harm it inflicts on the reef's denizens, illustrating their ability to defend themselves from UV damage.



Another example is the study done on "Naturally occurring nanoparticles from English ivy: an alternative to metal-based nanoparticles for UV protection" by the Department of Mechanical, Aerospace and Biomedical Engineering, University of Tennessee, Knoxville, TN, 37996, USA. Besides it's tested photo-protective capabilities, they speak about "the adhesive effect of the ivy's nanoparticles allowing the ivy nanoparticles to remain on human skin for a longer period of time, and thus enhancing their UV protective effect."

They concluded "with the data collected from this study, we have demonstrated the great potential of ivy nanoparticles as a sunscreen protective agent, and their increased safety over commonly used metal oxide nanoparticles."


Yet another example from nature is the single-cell alga called Dunaliella Bardawil, that thrives in the Dead Sea and the Sinai desert. It produces a yellow-orange pigment that shuns any excess light, which could interfere with its photosynthesis process - effectively acting as a sunscreen.

Researchers continue to try to gain approval for the many uses of natural ingredients in sunscreen formulations and I am sure we will see many more being highlighted and used in formulations as science turns more and more to how much nature has to teach us.

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