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Sunscreen is a non-negotiable year-round, but especially in warmer months when you’re spending more time outdoors and when the sun is stronger. When you peruse the offerings at your local chemist or fave online beauty shop, your head may spin from all of the options.

But apart from choosing an SPF number (hint: higher is better), what else do you need to know? And why does some sunscreen leave you with a ghostly glow? We’ve got your answers here.

How does SPF work?

The Argus: Before you pick out a sunscreen, you need to know how it works. Credit: Getty Images Before you pick out a sunscreen, you need to know how it works. Credit: Getty Images

For starters, it’s helpful to know how SPF works and why you should wear it every day. SPF, or sun protection factor, relates to the sunscreen’s ability to block UVB light, which is the wavelength responsible for sunburns. The higher the number following 'SPF', the higher percentage of UVB rays are blocked and the longer you can stay in direct sunlight without burning. To block UVA rays, which are linked to premature ageing, you want to look for the phrase 'broad-spectrum protection' on your sunscreen’s packaging. Both UVA and UVB rays cause damage to DNA cells that can lead to skin cancer.

To achieve SPF, companies use active ingredients that block or reflect away the sun’s damaging rays—referred to as physical sunscreens—or absorb and release their energy without allowing it to penetrate the skin, a.k.a., chemical sunscreens.

How do physical sunscreens work?

The Argus: You can go in the sun right away with physical sunscreens. Credit: Skinceuticals / Neutrogena You can go in the sun right away with physical sunscreens. Credit: Skinceuticals / Neutrogena

Physical sunscreens sit on top of the skin and deflect rays to keep them from penetrating the skin’s surface. They’re also called 'mineral' sunscreens, as they use zinc oxide and/or titanium dioxide to create a film over the skin to shield the skin from harm. They take effect immediately after application, rather than needing to soak in to achieve their full effect. On the downside, these physical ingredients can also be difficult if not impossible to fully blend in, leaving that telltale whitish cast on the skin.

The good news is, some companies make 'cosmetically elegant' SPF products containing ‘micronized physical blockers’ that won’t cause a ghostly appearance, explains Dr Suzanne Friedler, a board-certified dermatologist with Advanced Dermatology PC in New York City. It’s difficult to tell just from packaging and ingredients if a physical sunscreen will leave a white cast or if it’s ‘cosmetically elegant,’ but you’ll find keywords like ‘microfine’ or ‘micronized’ in product descriptions and these are helpful indicators, and you can also look to testimonials from online user reviews.

For example, reviewers say the SkinCeuticals Mineral Radiance UV Defense SPF 50 feels lightweight on the skin and looks ‘invisible’, making it worth the price. For a more budget-friendly option, the Neutrogena Healthy Defense Daily Moisturizer goes on pigmented but reviewers say it turns translucent when it’s massaged into the skin.

How do chemical sunscreens work?

The Argus: Let chemical sunscreen completely absorb into the skin before going out in the sun. Credit: Supergoop / Aveeno Let chemical sunscreen completely absorb into the skin before going out in the sun. Credit: Supergoop / Aveeno

Another option for avoiding a white cast is to choose a chemical sunscreen. These products contain active ingredients such as avobenzone, octisalate, and oxybenzone, which absorb into the skin and protect it by converting the sun’s UV rays into heat that’s then released into the air. The ingredients absorb into the skin instead of sitting on top of it the way that physical sunscreens do, so they’re less likely to leave a white cast. However, they typically take about 15 minutes to reach maximum effectiveness, so you must be even more diligent about reapplying so there are no gaps in your skin’s protection. Chemical sunscreens have also been associated with some controversy regarding what, if any, risks their absorption may pose to human health—for now, United States FDA says to continue using sunscreen, as the ramifications of not using it are likely riskier than any harm from absorption of the ingredients.

For a popular chemical sunscreen option, look to Supergoop’s Unseen Sunscreen SPF 30, which uses avobenzone, homosalate, octisalate, and octocrylene to protect the skin from the sun—and users rave about its smooth finish that layers seamlessly under makeup. For a great choice under £15, try the Aveeno Protect + Hydrate Face and Sunscreen Lotion, which moisturises with colloidal oatmeal and that satisfied customers say feels lightweight on the skin.

Which type of sunscreen is right for you?

The Argus: There's no right or wrong answer when it comes to choosing between chemical and physical sunscreens. Credit: Getty Images / LukaTDBThere's no right or wrong answer when it comes to choosing between chemical and physical sunscreens. Credit: Getty Images / LukaTDB

There’s no right or wrong answer, as both sunscreen types have one major benefit, when used correctly: protecting your skin from the damaging effects of the sun. If you’re unsure where to start, consider picking up an affordable sunscreen, such as the Neutrogena or Aveeno, to see if you like how it feels and what it looks like on your skin.

That said, there are hundreds of sunscreens out there, some that claim to moisturise dry skin and others that claim to keep oil at bay, and those are factors to consider as well. As long as you’ve got your skin covered, you can’t go wrong.

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Prices were accurate at the time this article was published but may change over time.