Tôi nên sử dụng SPF nào để bảo vệ khỏi tia UVA và UVB?
Sun protection can be confusing, and it’s important to know about SPF, UVA vs. UVB rays and other UV protection terms so you can decide what SPF to use. Consider this your guide to “What does SPF mean?”, reading sunscreen labels and understanding “broad spectrum,” “water resistant” and other sunscreen terminology so you can choose the right product to help protect your skin.
With terms such as UVA, UVB, SPF, broad spectrum and more, it can be difficult to understand sunscreen labels. However, this terminology provides key information about the type and level of UV protection your sunscreen provides. The U.S. Food and Drug Administration (FDA) has put several “rules” in place for sunscreen products, and these regulations cover acceptable ingredients as well as the wording that can be used on product labels. This means that once you understand sunscreen terminology1, you can read any label, regardless of the brand—which makes it easier to choose which sunscreen and which SPF are right for you.
- Broad-spectrum sun protection product helps protect your skin against both UVA and UVB rays.
- Sunscreen should be applied 15 minutes before exposing your skin to the sun – and reapplied at least every two hours.
- Physical, or mineral-based, UV ingredients like zinc oxide and titanium dioxide reflects UV rays.
UVA vs. UVB & Broad Spectrum
To understand UV protection, first you need to know the difference between UVA and UVB rays2, which are just part of the spectrum of light emitted by the sun—and there’s an easy way to remember how each of them affect the skin. UVA rays are considered “aging” rays because they can prematurely age your skin by causing wrinkles and discoloration, and these rays can penetrate glass. UVB rays are the “burning” rays, and these rays do not significantly penetrate glass. However, one thing that UVA and UVB rays have in common is that overexposure to either can lead to skin cancer in all skin types and ethnicities3. This is why it’s essential for you to use a broad-spectrum sun protection product4 that can help protect your skin against both UVA and UVB rays.5
What Does SPF Mean?
SPF stands for “sun protection factor,” but SPF only indicates protection against UVB, or “burning” rays. It may seem like an SPF of 50 provides almost double the protection as SPF 30, but that’s not the case. SPF 30 blocks 97% of UVB rays6 and SPF 50 blocks 98% of UVB rays.6
Since SPF only applies to UVB rays, it’s imperative to choose a sunscreen that says “broad spectrum” on the label, as this indicates the product helps protect the skin from UVA rays as well.5 Remember, a higher SPF does not mean you can spend more time outside without reapplying.
What SPF Should I Use?
The best sunscreen4 is a broad-spectrum formula that helps protect against UVA and UVB rays that you will use every day. Some sunscreen products can be specially-formulated to provide other benefits to the skin, such as extra moisture, and may contain beneficial ingredients like soothing niacinamide and ceramides to help restore your skin’s natural protective barrier.
How Does SPF Work?
Sunscreens with chemical-based ingredients, such as homosalate, work by absorbing UV rays before they can damage your skin. Physical or mineral-based UV ingredients like zinc oxide and titanium dioxide create a barrier on your skin’s surface that reflects UV rays. Some sun protection products include a mix of both chemical and mineral sun filters7—and you can learn more about these ingredients here. However, the key for optimal sun protection is proper application8, and it’s essential to apply an adequate amount of sunscreen to cover exposed skin and reapply as directed.5
How to Use Sunscreen
It’s important to keep a few additional application tips8 in mind to maximize the UV protection sunscreen can provide.
- Most adults need about one ounce, or enough to fill a shot glass, for the entire body—and don’t forget often-missed spots like the ears, tops of the feet and the back of the neck. Stick-based UV protection is helpful for smaller areas like around the eyes and the lips.
- When using sunscreen, it’s important to apply it 15 minutes before going into the sun. And, again, remember to reapply at least every two hours, or after swimming, sweating or towel-drying8.
Of course, when in doubt, read the instructions on the bottle or tube of your favorite sunscreen.