How Sun Protection Factor (SPF) works

Cómo funciona el Factor de Protección Solar (SPF)

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We all recognize the importance of protecting the skin with SPF products. But understanding how they actually work is a little more complicated. In this article, we will explain what SPF is, how long it lasts, and the different types of sunscreen available.

UVA and UVB rays

Solar radiation consists of UVA and UVB rays, which damage the skin in different ways. UVB rays only reach the surface of the skin and cause sunburn (redness), while UVA rays can penetrate deeper into the skin and cause DNA damage.

Sun Protection Factor

Sun protection factor (SPF) measures how much UVB protection a product provides to the skin. The higher the SPF, the more it protects. A product containing SPF 30 will protect the skin from almost 97% of the sun's UVB rays (when applied generously). SPF is a guide to how long you can stay in direct sunlight before your skin starts to burn.

To figure this out, you'll need to know how long it takes for your skin to turn pink without sun protection. If you normally burn after 10 minutes in the sun without protection, multiply this number by the SPF rating you are using. This is how long your sun protection will last. For example, if you burn within 10 minutes of being exposed to the sun without protection and you are using SPF 30, you will get 5 hours of sun protection (10 minutes x 30 = 5 hours).

While UVB rays are responsible for visible sun damage, you should also protect your skin against UVA rays. UVA rays are present all year round, regardless of the weather, and can penetrate windows and glass. This makes it really important to choose products with a broad-spectrum sunscreen that protects the skin from UVA and UVB rays.

Mineral and Synthetic Protection Factor


Synthetic or chemical sunscreens, such as homosalate or avobenzone, absorb UV radiation into the skin. They must be completely absorbed into the skin to work, so be sure to apply them at least 20 minutes before going outside. Chemical sunscreens tend to have a light texture, making them ideal for those with oily skin or skin prone to breakouts.


Mineral sunscreens, such as titanium dioxide or zinc oxide, work by reflecting UV radiation when it reaches the skin, creating a mirror effect. They work immediately after application, so you don't need to wait before going outside to sunbathe. If you have sensitive skin, mineral sunscreens are the best option as they are less likely to cause irritation.

When to reapply sunscreen

Sunscreen breaks down from direct exposure to daylight, so how often you should reapply sunscreen depends on the amount of time you spend outside. If you're in the office all day, the sunscreen you applied in the morning will still be effective when you return home at the end of the day.

If you spend more time outdoors in direct sunlight, you should reapply regularly, at least every 2 hours, to ensure you get full sun protection. If you're swimming or sweating, sunscreen will wear off more quickly (even if it's labeled waterproof) and you'll need to reapply it every 40 to 80 minutes.

See SPF Moisturizers