Whether you’re concerned about sunburns, skin cancer or premature signs of aging, wearing sunscreen every day is the best thing you can do for your skin. But how exactly does it protect your skin—and how do you pick the best formula for your needs?
We asked Dr. Monica Li, a Vancouver-based dermatologist and clinical instructor at the University of British Columbia’s Department of Dermatology and Skin Science, and Dr. Jennifer Beecker, a dermatologist in Ottawa and the vice-president of the Canadian Dermatology Association, to answer all our burning questions about SPF.
How does sunscreen work?
Sunscreen contains filters that work by absorbing or reflecting some of the sun’s UV radiation. There are two types of sunscreens: chemical and mineral. “Chemical sunscreen works by absorbing UV radiation and converting it to heat to provide sun protection, while mineral sunscreen reflects UV rays off the skin,” says Li. “Both types provide effective sun protection.” For people with sensitive skin, she recommends mineral sunscreens because they provide a physical shield between skin and the sun’s rays.
What is SPF—and how much is enough protection?
Beecker describes SPF—which stands for sun protection factor—as a multiple of how long it takes skin to burn. For example, wearing SPF 30 would prevent a sunburn 30 times longer than it would normally take to burn. “In Canada, we always recommend a minimum of SPF 30,” she says. She explains that since there’s only a slight increase of protection in SPF 40 and higher, SPF 30 provides an adequate amount of protection from the sun on an average day with minimal time spent outside.
What does “broad spectrum” mean?
The sun radiates two types of potentially harmful UV rays: UVB, which are responsible for sunburns and skin cancer, and UVA, which cause visible signs of aging and hyperpigmentation. Broad spectrum sunscreen protects from both UVB and UVA rays. “You want to look for a sunscreen that covers both,” notes Beecker.
What are the benefits of using sunscreen?
Wearing sunscreen is the best way to protect yourself against skin cancer. A study conducted in Australia found that there was a 40 percent decrease in the presence of squamous cell carcinoma (skin cancer) in participants who wore sunscreen every day compared to those who did not.
Sunscreen is also proven to prevent visible signs of aging, such as fine lines, dark spots and loss of firmness. “Sun exposure degrades collagen and elastin fibres, hence why skin may appear leathery and dull,” explains Li. People who do not wear sunscreen daily tend to see signs of aging much earlier than expected, adds Beecker. According to the Institute of Quality and Efficiency in Health Care based in Germany, UV radiation starts becoming harmful after just five to 10 minutes spent in the sun.
Should I wear sunscreen every day, even when I’m inside?
Yes, you should wear sunscreen on your face and other exposed areas when inside and all year round, even in winter. “We should think of applying SPF in the same way we approach brushing our teeth—it’s part of our daily self-care routine and an important healthy skin habit,” says Li, who also notes that UV rays can cause sun damage even on an overcast day or when reflecting off snow. UVA rays also penetrate glass, which is why Beecker stresses the importance of a broad-spectrum SPF, even when at home or in the car.
How do I incorporate SPF into my routine?
In general, it’s best to apply your sunscreen as the last step of your skincare routine, on top of your moisturizer and before makeup. Sunscreen should only be worn during the day, and thoroughly removed at night with a cleanser. “Moisturizers and foundations with SPF are adequate [as a main source of sun protection] if they have the recommended SPF and broad-spectrum protection,” adds Li.
According to Health Canada guidelines, you should use 35 mL of sunscreen (the equivalent of seven teaspoons) for the whole body, and a nickel-sized amount (½ teaspoon) for the face and neck alone.
How often should I reapply sunscreen?
Li stresses that sunscreen should be reapplied every two hours, or more frequently if you’re sweating heavily. But for most makeup fanatics, this can be difficult. For quick touch-ups, Beecker recommends opting for SPF-infused makeup products, like tinted moisturizer, powders and setting sprays. A slew of new powdered formulas that blend sun protection and base-perfecting powers have recently hit the market and make reapplication a breeze. Available both pressed and loose, these setting powders contain the same UV filters you’ll find in mineral sunscreens, like titanium dioxide and zinc oxide. (Unfortunately though, the shade range is still extremely limited.) While great for application over makeup, they should not be used as a primary source of sun protection. (But if you want to give it a whirl, we’re partial to the Canadian-made Dr. Renaud Cell’Defense Loose Powder SPF 50.)
This piece was originally published in 2021, updated in 2022.