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SPF Ratings - What Do They Actually Mean?

Posted by Amanda Soon on
 Zove Beauty - SPF ratings, What Do They Actually Mean?

Image Source: Pinterest

By Shilpa Bhim

Rain or shine, you should slather on your sunscreen. Those pesky UV rays will get you otherwise. 

But does anyone else feel confused about what level of SPF they need to wear? Like, what does SPF 30 actually mean? 

You know we take sunscreen very seriously here at Zove HQ. So let’s get into the nitty gritty of what the SPF ratings mean, with tips from some industry experts!


SPF stands for sun protection factor, and it’s designed to protect your skin from the sun’s harmful UV rays. 

There’s two types of UV rays that you need to look out for: UVA and UVB rays. Both are able to penetrate the skin and cause permanent damage to the cells.

Paige Preston, Chair of Cancer Council’s Skin Cancer Committee, breaks down the difference between the two types of UV rays:

UVA rays penetrate deeply into the skin (the dermis) causing genetic damage to cells, photo-ageing (wrinkling, blotchiness etc) and immune-suppression. 

UVB rays penetrate into the epidermis (top layer of the skin) causing damage to the cells and plays a key role in the development of skin cancer. UVB is also responsible for sunburn – a significant indicator of the damage likely to cause skin cancer.

Sunscreens work in two ways – they can contain ingredients that scatter UV radiation away from the skin (sometimes called physical sunscreens) or ingredients that absorb UV. 


SPF is basically a measure of how much time it takes for UVB rays to burn the skin, compared to skin that has no sunscreen. 

Fun fact, Michelle Wong from Lab Muffin Beauty Science shares that testing of sunscreens is performed on humans in a lab, using a UV lamp.

The number beside SPF on a bottle explains how well the sunscreen protects skin against sunburn. 

A simple formula is used to work out the SPF number - see, your teachers weren’t lying when they said you’d have to keep using maths as an adult!

The formula is the number of seconds it takes a patch of skin to slightly redden when covered in sunscreen, divided by the number of seconds it takes that patch of skin to slightly redden when there is no sunscreen applied. 

For example (and for easy maths), a sunscreen that’s labelled ‘SPF 30’ means that it took 300 seconds for skin to burn with sunscreen on, and 10 seconds to burn without it.


As Michelle Wong from Lab Muffin Beauty Science notes, “SPF means how many times more UV your skin can handle before burning with sunscreen on, compared to nothing at all.”

Preston recommends applying a “SPF30 or higher sunscreen that is broad spectrum, water resistant and TGA approved.”

Pro tip: all sunscreens sold in Australia are regulated by the Therapeutic Goods Administration which means they have met stringent guidelines that ensure they are safe and effective.

Wong agrees that a SPF 30 or higher broad spectrum sunscreen is the way to go, noting that SPF ratings on their own don’t really take UVA rays into account. Using a broad spectrum sunscreen (or one marked with a PPD rating) guarantees your sunscreen will protect you from ageing UVA and burning UVB rays.

If you’re wondering whether to go with SPF 30 or SPF 50, the main thing to note is that SPF30 blocks out 96.7% of UVB, while SPF50 blocks out 98% of UVB. So, both are pretty effective, and you’ll get just that little bit of additional protection with an SPF 50.

Most importantly, remember to apply your sunscreen evenly across your skin. Preston also notes that “sunscreen needs to be applied 20 minutes before going outdoors … Sunscreen should be reapplied every two hours if you are spending time outdoors and after swimming, sweating or towel drying.”

In addition to slopping on your SPF, don’t forget to “slip on protective clothing, slap on a hat, seek shade and slide on sunglasses.”

Have more questions about sunscreen and SPF ratings? Feel free to reach out to us via Instagram or email us - we love hearing from you!

Shilpa is a freelance beauty and lifestyle writer from Melbourne, Australia. You can keep up with her adventures over at @skb.ontherun and check out her latest articles here.

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