Sunscreens are products that prevent ultraviolet (UV) light from reaching the skin, thus protecting the skin against sunburn damage.
A quick note about UV rays:
(*The higher the wavelength-> less energy)
Sunscreen can be categorized into two sections depending on how they work. The first is chemical or organic sunscreen. Organic sunscreen’s mode of action is absorption. They absorb UV light and turn it into heat.
The second is physical or inorganic sunscreen. They also work by absorbing UV and some particles scatter and reflect UV light. Two materials used in this category are Titanium dioxide (TiO2) and Zinc oxide (ZnO).
Properties of the two types of sunscreen:
Organic sunscreen: achieve higher UVA (320-400 nm) protection, referred to as broad-spectrum.
However, organic filters may cause allergies and irritation to sensitive skin (depend on skin type and personal experiences). Common organic sunscreen agents: Ethylhexyl methoxycinnamate, avobenzone, octocrylene, Tinosorb S, Tinosorb M, etc…
Inorganic sunscreen: more gentle, and cause less irritation.
Titanium dioxide reflects primarily in the UVB region (290-320 nm). Zinc oxide reflects both UVA (320-400 nm) and UVB (290-320 nm) in roughly equal amounts. However, these two materials are bright white (especially TiO2), thus they do give white color when applied to the skin.
What is SPF?
SPF is known as a sun protection factor, which measures the amount of protection from UVB rays.
In other ways, SPF tells you how much UV exposure your skin can handle before it starts to get burned when you have sunscreen on compared to bare skin. For example, wearing sunscreen with SPF 30 basically takes your skin 30 times longer to get burned than when you don’t wear any sunscreen.
SPF 30 blocks 93% UVB rays
SPF 50 blocks 97% UVB rays
SPF 70 blocks 98% UVB rays
SPF 100 blocks 98.3% UVB rays
which means they still let some amount of UV rays in (including UVA).
Ideally, a sunscreen with higher SPF and a broad-spectrum gives your skin more protection. However, the effectiveness of your SPF depends on how well you apply it (even and enough amount).
The amount used in the SPF test is 2 mg/cm2. Thus to get the SPF protection on the label, you need to apply sunscreen with the amount of 2 mg/cm2 (about ¼ teaspoon for the average face). If you don’t apply enough and skip reapplying after being under the sun for a long time, the higher risk that your skin gets damaged (no one wants that 🙁 )
Choosing sunscreen?
Again, choosing organic or inorganic sunscreen depends on your skin type and your preference. You can choose based on their properties, which are mentioned briefly above. Indeed, the sciences behind how these sunscreen agents work are quite technically complicated, thus I just summarize it in a comprehensible way.
In short,
- Wear sunscreen even when you are not under direct sunlight (UVA rays can penetrate through the glass).
- Apply sunscreen enough and even. Reapply when needed.
Hope you find this information helpful.
Reference:
Benson, H., Roberts, M., et al., Cosmetic formulation: Principle and Practice, 2019, 280-285
How do sunscreens work, Lab muffin
https://labmuffin.com/how-do-sunscreens-work-the-science-with-video/
How much sunscreen is enough, The Doctor will see you now
https://www.thedoctorwillseeyounow.com/content/cancer/art5636.html
