What is SPF and How Does It Work?

What is SPF? | Arizona Dermatology It’s no secret that the Arizona sun is brutal. Sunscreen is an essential part of living in the desert, and regular use of sunscreen plays a vital role in prevention against skin cancer. While it’s important to apply sunscreen daily, it’s also important to understand what SPF is and how it contributes to the effectiveness of your sunscreen.

What is SPF?

SPF, or sun protection factor, is used to measure the amount of protection sunscreen provides against the damaging UVB rays from the sun. SPF does not measure protection from UVA rays, although many sunscreens protect against both.

Another way to think of SPF is as a multiplication factor to help you determine how long you can stay in the sun without developing a sunburn. For example, if you usually spend 20 minutes in the sun without burning, SPF 15 will allow you to stay in the sun 15 times longer—about 5 hours. However, keep in mind, the exact amount of time you can spend in the sun without developing a sunburn will depend on factors like the color of your skin and your age.

UVA and UVB: What’s the difference?

UVB (ultraviolet B) rays cause sunburns and contribute to skin cancer. UVA (ultraviolet A) rays contribute to photoaging. Photoaging is premature aging of the skin. It includes the sun spots and wrinkles many develop from prolonged sun exposure, but it can also include skin cancer.

Because of this, it’s important to use sunscreen that has broad coverage, providing protection from both the sun’s UVA and UVB rays.

What do SPF numbers mean?

Oftentimes, SPF is associated with a number. This number represents the amount of protection the sunscreen provides. This associated number can be as low as five, offering minimal protection, but can also be as high as 100, offering maximum protection.

Three of the most common levels of SPF are 15, 30, and 50.

  • SPF 15 blocks 93% of UVB rays
  • SPF 30 blocks 97% of UVB rays
  • SPF 50 blocks 98% of UVB rays

How much SPF do you need?

With such a wide range of SPF available, it can be easy to be confused about how much SPF you actually need. We recommend using sunscreen with at least SPF 30 every day, even when it’s cloudy.

How to apply the right amount of sunscreen

If you don’t apply the right amount of sunscreen, you’ll only receive a fraction of the SPF promised by the bottle, leaving you more vulnerable to the sun’s ultraviolet rays.

For appropriate protection, we recommend applying one ounce of sunscreen to your body, and a nickel-sized amount to your face. Remember to also apply sunscreen to areas that are commonly overlooked, including the top of your feet, back of your neck, and ears.

Remember to reapply

Regardless of its SPF rating, no sunscreen will keep its full effectiveness for longer than two hours of continuous sun exposure without reapplication. To get full protection from the damaging effects of the sun’s rays, we recommend reapplying your sunscreen every two hours, after continuous exposure to the sun.

What sunscreen is right for you?

We recommend selecting a broad spectrum sunscreen with an SPF of at least 30. Aside from this recommendation, the choice of sunscreen comes down to personal preferences. The right sunscreen for you may vary depending on your preference between physical or chemical sunscreens, as well as the level of protection necessary for your daily activities.

Physical vs. chemical sunscreens

Chemical sunscreens utilize compounds that absorb the sun’s rays without harming your skin. These sunscreens commonly use chemical ingredients like avobenzone and oxybenzone to protect your skin. Chemical sunscreens are ideal for those with oily skin, as they commonly mattify skin tone and texture.

On the other hand, physical sunscreens physically block and reflect ultraviolet rays away from your skin. These sunscreens use common ingredients like titanium dioxide and zinc oxide and are ideal for those with sensitive skin or those with skin conditions like rosacea.

Daily use vs. active use

If you spend most of your day indoors, you may only need to be protected from incidental sun exposure. Incidental sun exposure occurs in short periods of time, like walking from the parking lot to your office, driving, sitting near a window, or walking your dog. For these purposes, any broad spectrum sunscreen with at least an SPF of 30 will keep you protected.

However, if you plan on spending most of your day outdoors, you’ll need to be protected from extended or active sun exposure. For this protection, we recommend applying sunscreen with water resistance, which will keep you protected even when swimming or sweating. Most sunscreens for these purposes will be labeled as “outdoor” or “sport” sunscreens.

Beyond sunscreen

Sunscreen is only one piece of the equation. To stay fully protected from the sun, it’s important to keep other preventative steps in mind. For example, we recommend wearing protective clothing like sunglasses, wide brimmed hats, and shirts made from fabrics like linen. We also recommend limiting outdoor activities when the sun is at its midday peak between 10am-2pm. It’s also important to avoid any form of tanning or tanning beds. A tan is just another form of sun damage.

It’s never too late

A common misconception is that damage from the sun cannot be reversed. This is far from the truth. In reality, many forms of sun damage can be lessened or even reversed with treatments like chemical peels.

It’s never too late to start being proactive about sun protection. With time, skin becomes more vulnerable to sun damage, making sun protection even more important. If you haven’t been wearing sunscreen thus far, don’t worry. It’s not too late. Start applying sunscreen now—your skin will thank you later.

Your next steps

If you have any questions about SPF, sunscreen, sun damage, or skin cancer, we’re here to help. Our experts can recommend treatments or products and give sound, professional advice. Schedule a consultation appointment today to get started.