What does SPF mean?

So you’re in the market for a new 100% organic and natural sunscreen but you’re not sure what to look for? For most people, the default is to grab the bottle with the highest SPF. Bigger is better, right? But what do those SPF numbers actually mean?

SPF stands for “Sun Protection Factor”, and the number beside it indicates how well the sunscreen protects skin against sunburn. It is not an indicator of how long you can stay out in the sun, rather, it indicates how much longer it takes untanned skin to start to redden with sunscreen applied compared to how long it takes to start reddening without it. The Noosa Naturals 100% Organic and Natural Sunscreen range is Broad Spectrum UVA/UVB SPF 50.

Sun Protection Factor

To work out the SPF of a sunscreen, laboratory tests are carried out on an untanned patch of skin of human volunteers. Sunscreen is applied liberally to the skin, which is then exposed to simulated sunlight via UV lamps. Measurements are taken of how long it takes the skin to redden when covered with sunscreen, and how long it takes to get the same redness without it.

determine the SPF

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

Say it took 500 seconds for skin to burn with sunscreen, and 10 seconds to burn without it, 500 is divided by 10, which is 50. Hence, the SPF is 50. 

In terms of UV filtration, SPF 15 blocks approximately 93% of UVB radiation, while SPF 30 comes in at about 97% and SPF 50 at 98%. It is important to note however that these values only apply if the sunscreen is applied properly and at regular intervals.

So what do these SPF terms actually mean? Let’s break it down..


The SPF (Sun Protection Factor) of a sunscreen is a measure of how well it protects the skin from sunburn. Sunscreens need to be applied liberally and regularly to achieve the SPF protection claimed on the label.

Water resistant: 

Sunscreen does not come off the skin during swimming or exercise, provided it is not physically wiped off. While a label may state a sunscreen is ‘4 hours water resistant’, sunscreen still needs to be applied every two hours to maintain the same level of protection.


Broad-spectrum sunscreens filter both UVA and UVB rays. UVB is the principal cause of sunburn, but both UVA and UVB contribute to increased skin cancer risk.

The '+' sign after SPF:

The plus sign means ‘more than’. For example, SPF50+ sunscreen must provide at least SPF60 in testing. This is because the same batch of sunscreen will test slightly differently in different laboratories with different methodology. By testing at SPF60, it removes any margin for error. 

Whether you’re wondering which SPF is best for the face, or the body, Noosa Naturals always recommends the highest available protection and has a range of products to suit the face and body. 

Considering the lifetime dangers of accumulated sun damage, it should come as no surprise that you need to wear sunscreen every day.

Head to the Noosa Naturals product range to choose what suits you and your skin best.