How Sunscreens Work

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Have you ever stayed outside for a couple of hours in the middle of the day, when you went out to the beach with friends, or had a picnic in the park, and come back indoors to find that your skin has become a little darker, or redder, and after a few days discovered tiny little dark spots on your arms, cheeks or nose? 

These visual clues are usual signs of UV damage that we get from the unprotected sun exposure. With mild exposure, these effects usually go away after a few days, but with more severe exposure, the effects may be more far reaching and worrisome as it can lead to long-term skin damage.

One sure way we can prevent this damage from occurring is by reducing our exposure to UV light i.e. not going under the sun when the UV index is Level 4 and above (more on this in another post), and by donning physical barriers to protect exposed parts of our skin, like long-sleeves, wide-brimmed hats, and sun glasses. These work best as their protection does not get wiped off or washed away, is always even, and doesn't need reapplication.

For parts of our skin that remain uncovered, like our face, neck, or in the absence of those mentioned above, sunscreens are the next best thing.

Sunscreens work by reducing the UV light that gets into your skin, and it does so through the electrons in its active ingredients that absorb the UV, which convert the light energy into other less harmful forms of energy.

These electrons react to specific UV wavelengths, thus it is necessary to include UV filters or ingredients that are a match to the specific wavelengths that are we’re trying to avoid. The absorption process occurs when a stable sunscreen molecule on our skin receives UV energy from the sun and causes it to get excited. In order to return to its normal relaxed state, it absorbs the UV energy and then emits the same amount of energy, usually in a different form. 

To illustrate this point, we can use fireworks as an example. Electrons receive heat from the pyrotechnics, and release it as light energy. A specific type of chemical releases a  specific type of light, so should you want yellow light to be released, you put in barium. For orange light, you put in strontium, for purple light you put in a combination of strontium and copper, and so on.

This released energy usually takes of three forms: vibrations, which becomes heat, light, which takes the form of infrared visible light, or other less harmful lower energy UV, and chemical energy, which result in breaking chemical bonds.

Given that the two types of UV found to cause us photodamage are UVA and UVB, the specific actives or filters in our sunscreen have to be of a structure that attenuates those rays. UVA is of a longer wavelength and lower energy, and the exposure to this is commonly associated with accelerated signs of skin ageing. UVB on the other hand, is of a shorter wavelength and higher energy, is evidenced by sunburns and sunspots.

For more information on the topic, read on to our next post on the How Sunscreens Work series!

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