Dermatology and Skin Care Updates from Waterhoody

How Does Sunscreen Work?

How Does Sunscreen Work?

This is the first of a 4 part series on sunscreen.

  • Part 1: How does sunscreen work?
  • Part 2: What does SPF mean?
  • Part 3: What does “broad spectrum” mean?
  • Part 4: Does using an SPF greater than 30 make a difference?


Part 1: How does sunscreen work?


Sunscreen is made up of particles that are able to absorb the sun’s rays before they hit your skin.  This prevents most of the sun’s dangerous radiation from causing damage to the DNA of your skin cells—damage that could otherwise lead to skin cancer and skin aging.  When the sunscreen’s molecules absorb the UV light, they are converted to inactive particles that can no longer absorb the radiation.   As there are a finite number of sunscreen particles on your skin, eventually most of them are deactivated by the sun’s radiation and the sunscreen loses it’s ability to protect you.  This is the main reason you should reapply sunscreen after about 2 hours of sun exposure. Sun protective (UPF) clothing is an effective alternative to sunscreen as it does not lose it’s sun protective abilities throughout the day and provides lasting protection. Of course, you would still want to use sunscreen on areas not covered by UPF clothing.

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