What Is SPF and How Does It Work?

Let’s start with the basics. “SPF” stands for Sun Protection Factor, and it measures how well a sunscreen protects your skin from UVB rays, the ones responsible for sunburn and surface-level skin damage. The number refers to how much longer it would take your skin to burn with the product on vs. without it. For example, SPF 30 means it would take you 30 times longer to burn.

But here’s the twist: SPF doesn’t offer linear protection. 

• SPF 15 blocks about 93% of UVB rays, 

• SPF 30 blocks 97%, 

• SPF 50 blocks 98%.

That extra percentage point can make a difference if your skin’s especially sensitive or you’re simply seeking every advantage in the pursuit of flawless skin.

UVA vs. UVB Rays: Know Your Enemies

Think of UVB as the sunburn ray and UVA as the ageing ray. UVA rays penetrate deeper into the skin, causing fine lines, pigmentation, and long-term collagen breakdown. Unlike UVB, they can pass through glass. This is why "broad-spectrum sunscreen” is key; it means your product protects against both UVA and UVB.

If you're into Korean sunscreens, you might recognise UVA protection by the “PA” rating system: short for Protection Grade of UVA. The more plus signs, the higher the protection: PA+ offers some UVA defence, while PA++++ provides the strongest level. So if you're serious about anti-ageing, pigmentation control, or glass skin goals, keep an eye out for those extra +'s.

Understanding Different Types of Sunscreen

When it comes to formulation, sunscreens generally fall into two camps: chemical and mineral/physical. 

Chemical sunscreens use ingredients like avobenzone or octisalate to absorb UV rays and convert them into heat. They're lightweight, usually invisible, and beloved by make-up wearers for their smooth finish. 

Mineral sunscreens use zinc oxide or titanium dioxide to sit on the skin’s surface and physically deflect rays. They're a godsend for sensitive skin, but older formulas often left behind an unflattering chalky cast. Thankfully, modern mineral SPFs have evolved, especially tinted versions, which use iron oxides to counter the white cast and even help protect against visible light. This makes them particularly useful for darker skin tones, which are more prone to hyperpigmentation. 

Is one better than the other? Not necessarily. It’s all about what works for your skin and your lifestyle. The best SPF is the one you’ll use liberally and daily.

And no, melanin is not enough to forgo sunscreen altogether. While it does offer some natural defence, it’s not nearly sufficient to prevent long-term sun damage.

SPF for Kids

Children, meanwhile, need their own approach. Their skin is thinner and more absorbent, so mineral sunscreens are safest, ideally SPF 30 or above, water-resistant, and free from potential irritants like fragrance or alcohol. Babies under six months should be kept out of direct sunlight altogether, with physical barriers (think umbrellas and wide-brimmed hats) doing most of the work.

Everyday vs. Holiday SPF

Contrary to popular belief, sunscreen isn't just a holiday essential; it’s an everyday one. Even on grey, cloudy days or while sitting indoors near windows, UVA rays can still reach your skin. So yes, you absolutely should wear SPF inside, particularly if you spend time near natural light or are concerned about blue light exposure from screens. While research is ongoing, visible light (especially in the blue spectrum) may contribute to pigmentation issues in some skin types.

For daily city wear, an SPF 30 with broad-spectrum protection is generally sufficient. But for long outdoor days, seaside escapes, or alpine adventures, bumping up to SPF 50 offers extra reassurance. The same goes for post-treatment skin: after a peel, laser, or microneedling session, higher protection is non-negotiable.

The Art of Application: How to Get It Right

Here’s the truth: most people use far too little sunscreen. For the face alone, you need about a teaspoon, roughly two fingers’ length. For the body, aim for a 6 to 8 teaspoons. And it’s not a once-a-day affair. The question is how long does sunscreen last? It wears off due to sweat, water, and friction, so you’ll need to reapply every two hours, or immediately after swimming or towelling off.

And don’t forget the easy-to-miss areas: ears, neck, décolletage, hands, the tops of feet. Your lips, too, use a dedicated SPF balm. Sensitive scalp? A spray or powder SPF is perfect for partings and hairlines without the greasiness.

If you wear makeup, reapplying might feel impossible, but there are clever ways to do it. Use an SPF mist, cushion compact, or powder sunscreen designed for touch-ups without disturbing your base.

Common Mistakes Even the Best of Us Make

One of the biggest pitfalls? Relying on sunscreen in makeup alone. While foundations and primers often boast SPF 15 or 20, you'd need to apply a thick layer to get the labelled protection—and who’s doing that? Think of SPF makeup as your backup, not your front line.

Another common misstep is using expired products. Does sunscreen expire? Absolutely. Like all skincare, it goes bad eventually. Most formulas last around three years unopened, but once opened, aim to use them within 12 months. If it smells off, looks separated, or the texture has changed, ditch it.

And yes, sunscreen can (and should) be used year-round, not just in summer. Winter sun, especially when reflected by snow, can be just as damaging. Your skin doesn’t hibernate, and neither should your SPF.

FAQs

How do you remove sunscreen from clothes?

Sunscreen stains are often caused by the oils and mineral filters in the formula. To lift them, act quickly: blot (don’t rub) any excess, then pre-treat the stain with a grease-fighting liquid detergent or dish soap before washing. Avoid bleach, especially on light fabrics, as it can react with certain sunscreen ingredients and worsen discolouration. Warm water tends to work better than cold for breaking down oil-based formulas.

How do you get rid of sunscreen stains?

For stubborn yellow or orange stains, particularly those on white clothing caused by avobenzone reacting with iron in water, try soaking the garment in a mix of water and white vinegar or a laundry booster like oxygen bleach. Always check the care label first, and test a small area before applying any stain treatment to delicate or luxury fabrics.

Does sunscreen stop you from tanning?

Sunscreen doesn’t completely block UV rays; it significantly reduces exposure but doesn’t eliminate it. That means you can still tan while wearing SPF, especially if you’re using a lower factor or not reapplying often enough. The higher the SPF, the more it limits tanning and, importantly, the more it protects your skin from damage. If you're seeking a bronzed glow, a sunless tanning lotion is a safer option.