more about spf and why it matters

We all know we should wear sunscreen. But SPF is often treated as something we reach for on beach days, holidays, or when the sun is obviously shining.

The reality is that protecting your skin from ultraviolet (UV) radiation is about much more than avoiding a sunburn. UV exposure is one of the most important preventable causes of skin damage and skin cancer, and protecting your skin consistently can help reduce the risks associated with excessive sun exposure.

So, what does SPF actually do — and how can you make sure you're using it effectively?

what is UV radiation?

Ultraviolet radiation is invisible radiation emitted by the sun. The two types most relevant to everyday skin protection are UVA and UVB.

UVB is strongly associated with sunburn and plays an important role in the development of skin cancer. UVA penetrates deeper into the skin and is also associated with skin damage and premature skin aging. Broad-spectrum sunscreens are designed to provide protection against both UVA and UVB radiation.

Unlike visible light, you cannot see or feel UV radiation. That is part of what makes it so easy to underestimate.

The World Health Organization recommends taking particular care when the UV Index is 3 or above, because the higher the UV Index, the greater the potential for UV-related damage.

UV exposure is about more than sunburn.

Sunburn is an obvious sign that your skin has received too much UV radiation, but UV exposure can have effects beyond the temporary redness and discomfort we associate with getting burned.

According to the WHO, excessive UV exposure is a major cause of skin cancer and can also contribute to harmful effects on the eyes and immune system.

UV exposure is also associated with premature skin aging. The FDA notes that spending time in the sun without adequate protection increases the risk of both skin cancer and early skin aging.

That means sunscreen isn't simply about looking after your skin today. It is also part of taking care of your skin over the long term.

what does spf actually mean?

SPF stands for Sun Protection Factor.

It primarily describes protection against UVB-related sunburn. It is important to remember that SPF alone does not describe the full spectrum of UV protection, which is why choosing a broad-spectrum sunscreen is important when you want protection against both UVA and UVB.

For everyday use, many health authorities recommend choosing a sunscreen of at least SPF 30 and using it alongside other forms of sun protection such as shade, clothing and a hat.

the problem isn't always the spf. It's how we use it.

You can buy an SPF 50 sunscreen and still end up with inadequate protection if you don't apply enough or apply it unevenly.

The WHO notes that many people do not apply sufficient amounts of sunscreen to achieve the level of protection indicated on the product.

This is one of the biggest challenges with sunscreen: you can't easily see whether you've applied it evenly.

You look in the mirror and your skin simply looks... normal.

You can't see whether you've applied enough around your nose, along your hairline, around your eyes or on other exposed areas.

And once you're outside, sunscreen can also be affected by sweating, swimming, drying yourself with a towel and everyday rubbing or contact.

why reapplying spf matters

Sunscreen isn't something you apply once in the morning and forget about for the rest of the day.

The WHO recommends reapplying sunscreen approximately every two hours, particularly after sweating, swimming, exercising or other activities that can remove sunscreen from the skin.

Cancer Research UK similarly recommends regular reapplication, including after swimming, sweating or towelling off.

Importantly, reapplication isn't just about putting another layer over the same perfectly protected skin. Reapplying also gives you another opportunity to cover areas you may have missed or where your sunscreen coverage has become uneven.

what about cloudy days?

Clouds don't mean that UV radiation disappears.

UV levels vary depending on factors including time of day, season, location and weather conditions. Some UV radiation can pass through clouds, which is why checking the UV Index can be more useful than simply looking outside and deciding whether it "feels sunny."

When the UV Index is 3 or above, the WHO recommends taking protective measures against UV exposure.

So yes — sunscreen can still matter when the sky is cloudy.

see your sunscreen differently

There's one frustrating thing about sunscreen:

you can't see it.

You can apply it carefully, look in the mirror and think you've covered everything — but a normal mirror can't show you where your sunscreen coverage may be uneven.

That's where UV imaging can offer an interesting perspective.

Some sunscreens have ingredients that interact with UV light in a way that can make areas of sunscreen coverage visually distinguishable under suitable UV imaging. This can allow you to see differences in coverage that aren't obvious in ordinary visible light.

Karliie was created around this idea.

Our SPF Mirror uses a UV camera to give you another way to look at your sunscreen coverage — helping you spot areas that may need more attention before heading outside or when reapplying.

apply. check. protect.

Because good sun protection isn't just about owning sunscreen.

It's about using it consistently, applying it generously and evenly, and remembering to reapply.

Your skin is worth protecting today — and for all the years to come.

see your SPF differently with Karliie.