How Sunscreen Actually Works

Sunscreen is to skincare what salt is to cooking—without it, your skincare regimen will always be lacking something. That’s because the sun is responsible for a lengthy list of top skin concerns—it causes 90% of wrinkles, triggers hyperpigmentation and, without it, Melanoma would be a very rare disease.

Of course, without the sun, life wouldn’t exist. Nor would pool parties, rooftop drinks, or the “magic hour”. We love the sun, but we also love educating people on proper protection.

Here’s our definitive, science-baked guide to sunscreen.

UVB vs. UVA Radiation

The sun emits two types of ultraviolet rays: UVA and UVB. UVB rays damage the top layer of your skin and are responsible for burning. UVA rays penetrate to deeper layers of your skin and damage collagen, leading to wrinkles.

• UVB rays: mostly blocked by clouds and windows.
• UVA rays: not blocked by clouds and windows. This is why daily protection is important no matter the weather and no matter the season.

What do those SPF numbers really mean?

SPF stands for Sun Protection Factor. The numbers reference how much protection a product provides against UVB rays relative to how easily your skin burns. For example, if you generally burn after 10 minutes of unprotected sun exposure, a product with an SPF rating of 30 will allow you to stay in the sun for five hours without burning (10 minutes X 30). Contrary to popular belief, SPF 30 is not twice as protective as SPF 15. Here’s a breakdown of UVB protection as it relates to SPF number: 

SPF 15 = blocks 93% of UVB rays

SPF 30 = blocks 97% of UVB rays

SPF 50 = blocks 98% of UVB rays

Notice that we only mentioned UVB rays? The SPF number on sunscreen has nothing to do with UVA—those nasty rays that cause wrinkles. For that, you need to make sure that your sunscreen formulation is Broad Spectrum, which means the product will block both UVB and UVA. While you’ll likely see the words “Broad Spectrum” plastered on the front label, like all things in skincare, you have to analyze the ingredients to ensure what you’re getting is legit. These are the best Broad Spectrum ingredients, ranked from most protective to least protective:

1. Zinc Oxide
2. Titanium Dioxide
3. Avobenzone
4. Oxybenzone

Which ingredients you’re getting depends on the type of sunscreen you’re using. There are two types:

Physical sunscreen

Physical sunscreens are formulated with active mineral ingredients, most commonly Zinc Oxide and Titanium Dioxide. It works by creating a barrier that reflects UVA and UVB rays away from your skin before they cause damage. 

Pros of physical sunscreen:

• Starts working immediately
• Offers the broadest range of protection
• Less likely to cause irritation
• Less likely to clog pores

Cons of physical sunscreen

• Can rub off or run off from sweat
• Physical sunscreens have a reputation of being heavy and hard to rub in, but formulations have come a long way.

Chemical sunscreen

Chemical sunscreens are formulated with organic compounds like Avobenzone and Oxybenzone. These compounds penetrate your skin and absorb UV rays before they’re able to cause damage.

Pros of chemical sunscreen:

• Tend to be lightweight and spread easily
• Less is needed to protect your skin
• Often more sweat resistant than physical sunscreens

Cons of chemical sunscreen:

• Require 15-20 minutes before working
• Can cause irritation depending on the formulation and your skin type
• More likely to clog pores