The Science of Sunscreen

Why do we wear sunscreen?

Chances are, at one point or another in your childhood (or adulthood), you’ve been instructed to wear sunscreen when spending long periods of time outside in the sun. But have you ever considered the science behind this logic? Well no worries, I am here to save the day and share the scientific explanation behind this often misunderstood concept!


Science debunked!

I have dark skin. I don’t need sunscreen.

MYTH. Dark skin is just as susceptible to sun damage. In fact, it’s just more difficult to visually see the skin damage on the skin. Skin cells respond to UV rays by releasing pigment. This pigment, which we think of as a sunburn, is harder to see in darker skin. Your skin color is not the same as SPF sun protection!

-I don’t need sunscreen if it’s cloudy out or it’s cold.

MYTH. Clouds are simply water vapor. They can’t protect you from UV rays from the sun. People tend to hold the misconception that since it’s not sunny outside, there’s no way the sun’s rays could damage one’s skin. Newsflash! When you’re out skiing in the snow, you’re actually getting hit by the sun’s rays twice because the UV rays are being reflected; once from the sun and then when the sun’s rays bounce off the snow. This same phenomenon occurs on a cloudy day at the beach; you get hit by the sun’s rays directly and when they bounce off the water or sand.

-My sunscreen is SPF 50 so I don’t need to apply it as often.

MYTH. No matter what the SPF number is, sunscreen is only effective for around two hours maximum. The number refers to how much protection you’re actually getting from applying the product, not how long it lasts.

This visual reiterates what I stated above regarding what SPF numbers actually mean. The SPF value refers to how much protection one is receiving, NOT the duration of time it lasts.


Sunscreen is just a lot of applied chemistry!

A short synopsis of the science behind sunscreen:

  • UVA waves: About 95% of all solar radiation that reaches earth’s surface. It is also the kind of UV wave that penetrates deepest in our skin. Contributes to skin cancer through indirect DNA damage.
  • UVB waves: About 5% of all solar radiation that reaches earth’s surface. Causes direct DNA damage and one of the main contributors to skin cancer.

In order to be most effectively protected from the sun, the American Academy of Dermatology recommends looking for the “broad spectrum” label when purchasing a new bottle of sunscreen. Broad spectrum simply means that it will protect your skin from both UVA and UVB rays.

This infographic gives an even more in depth look into the chemistry of the various types of UV rays and their impact on the human body.


Below are some of the super informative websites I used to learn about the science behind sunscreen. Check them out to learn more about sun exposure and sunscreen!

Most of all, enjoy the summer solstice tomorrow!

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