Sunblock / Sunscreen

What does sunblock do?

It prevents UV radiation from interacting with cells in the dermal layer of your skin. To do this, it uses two kinds of chemicals:

  • Inorganic chemicals
    • Physically reflects UV rays when the sunblock is layered over your skin
  • Organic chemicals
    • Absorbs UV radiation through chemical bonds and releases heat

What is SPF?

As a rule of thumb:

<your default skin burn time> x SPF = <protected skin burn time>

Which means, if you typically burn in 20 minutes, then an SPF 15 will yield:

10min x 15 = 150min (2.5hrs)


  • A higher SPF does not mean a higher protection level
  • Sunscreens with higher SPF must be continually (every 2hrs) reapplied to stay effective on the skin

Why for we need sunblock?

History lesson time:

  1. Humans lived near equator
    • Skin was acclimated to block sun’s UV rays ☀️
    • Lots of sun and yummy Vitamin D
    • No need for sunblock
  2. Humans migrated away from equator
    • Skin naturally blocked sun’s UV rays
    • Lacked getting Vitamin D
      • Poor health 🤕
  3. Humans started going back toward equator
    • Skin not acclimated to block sun’s UV rays anymore 🔥