When choosing a sunscreen, most people choose it based on the SPF value on the front of the bottle.
This value is often associated with the level of protection that the sunscreen offers. While this is partially true, SPF is actually considered an unreliable method of measuring a sunscreen's effectiveness.
What does SPF Mean?
SPF is an acronym that stands for 'Sun Protection Factor', a formula for determining the fraction of UVB rays that will reach the skin over time, UVB rays being the ultraviolet radiation from the sun that burns your skin.
For example, an SPF15 sunscreen allows 1/15th of the UVB rays to reach the skin when applied correctly, while an SPF30 sunscreen allows 1/30th of the UVB rays to reach the skin.
What SPF Doesn’t Measure?
It is important to note, that SPF only measures against UVB rays. The sun also puts out UVA rays.
UVA rays travel through clouds and even windows, which normally stop UVB rays. This is very important to realise as you can be wearing extremely high SPF protection and have no protection from UVA rays, which account for 95% of the sun's ultraviolet radiation and cause skin aging, wrinkles and cancer in a process called photoaging.
How Long it Lasts
The other really important factor to realise about SPF is that the rating has no impact on how long it lasts on the skin. High SPF Sunscreens do not last or remain effective on the skin any longer than a lower SPF sunscreen, and must be reapplied as direct with the same frequency as even the lowest SPF sunscreen. Usually this is every two hours.
What's Wrong With SPF50?
Did you know the Cancer Council recommends SPF30 or above, not SPF50?
When we hear a number like 50 compared to 30, it sounds much higher, almost double in fact.
However in terms of SPF protection, this couldn’t be further from the truth.
To offer an accurate perspective we need to look at the percentages. You can see the percentage of UV radiation that still reaches the skin by putting the fraction into a calculator. For example for SPF50, 1/50th is 2%, meaning SPF50 prevents 98% of the UVB radiation from reaching the skin, while SPF30 prevents 96.7% of the UVB radiation from reaching the skin.
That's only a 1.3% difference between SPF50 and SPF30.
When you see this 1.3% difference, combined with the fact that SPF50 needs exactly the same application frequency as SPF30 or even SPF15. It becomes obvious that there is actually very little difference between the two.
In order to raise the SPF level higher, any UVA protection that may be provided is normally compromised for the greater UVB protection. Offering higher protection for 5% of the sun's ultraviolet radiation, while the 95% is left.
There is nothing inherently wrong with SPF50 or above in sunscreens, the danger is the perceived additional protection. When people use SPF50, they see themselves as having a significantly higher level of protection. This often leads to compromises in other areas, like not applying enough sunscreen or not reapplying frequently enough.
What the World Health Organisation Says
The world health organisation recommends a broad spectrum sunscreen, of SPF15 (93% Protection) and above.
Phillippe Autier is one scientist specialising primarily in research on cancers including skin cancer, used to be part of the World Health Organisation's agency for research on cancer. He has conducted several studies into behaviour with sun protection.
He found in multiple studies that people given higher SPF sunscreen had 'profound changes in sun behaviour'.¹
Does How Much Sunscreen I Put On Impact the Rating?
Yes. The amount of sunscreen you put on has a direct impact on the SPF value you end up receiving.
Studies show that applying half of the recommended amount of sunscreen, provides the square root of the SPF value in protection.
Put simply, applying half the correct amount of a SPF50, only gives you SPF7 protection.
Applying the Correct Amount
To apply the correct amount, experts recommend 2mg per cm² of skin, or more simply this usually equates to about a teaspoon per area covered.² For example, a teaspoon per arm, or a teaspoon for your neck, face and ears.
What SPF Should I Use?
In short, SPF is generally not the most important factor when choosing a sunscreen, and can often be misleading. But when you are choosing an SPF rating, we recommend SPF30, which as suggested by the Cancer Council, is more than adequate even for people with skin that burns very easily.
More important than SPF is that you choose a sunscreen that offers equal protection from UVA and UVB radiation, usually these are known as broad spectrum sunscreens.
How is a SPF Rating Determined?
There are many different methods for testing the SPF of a product. This is one of the arguments that SPF is an ineffective measurement of effectiveness.
The most common method for testing SPF is to apply it to the skin of a volunteer and measure how long before sunburn occurs when exposed to an artificial light source. There are also a series of spectrophotochemical methods and methods that use a spectrometer.
How Did We Arrive at SPF Ratings?
During 1974, an Austrian chemist named Franz Greiter introduced the term 'Sun Protection Factor' or SPF as part of marketing his sunscreen brand 'Piz Buin'.
SPF has since become a standard for measuring UVB protection, despite being misleading.
In Australia the Therapeutic Goods Administration capped SPF at 30, due to the misleading nature of higher SPF products. However in 2012 they increased the limit to SPF50+ under increasing global pressure.
The EU went through a very similar process and currently limit SPF on sunscreen labels to SPF50+.
In the United States the FDA (Food and Drug Administration) has contended since 2007 that SPF higher than 50, is inherently misleading.
Frequently Asked Questions
Can SPF reverse aging?
A few studies have indicated that it is possible to reduce photoaging of the skin through regular use of a broad spectrum sunscreen.³
In another study, broad spectrum sunscreen applied regularly has been shown to prevent skin aging.⁴
Although there is no evidence that different SPF values influence this.
What does the plus sign after the SPF number mean?
The plus sign after the SPF number is an indicator for a SPF rating higher than the number. For example if a sunscreen has an SPF30+ then the SPF rating is higher than 30.
Are SPF sprays effective?
This is a complicated question. Essentially yes they are just as effective in a laboratory with set spray time, however practically they are not.
A study done by the Queensland University of Technology showed that in order to spray an adequate dosage to meet its SPF value, the spray needed to be used for between 63 and 98 seconds.
This gave the sunscreen cans tested a maximum of two to three uses before being empty.⁵
Remembering how important application amount is to achieve the SPF rating of protection, it's obvious that while spray sunscreens can be just as effective as regular sunscreen lotion, they normally aren't when applied intuitively.
As a related note, in Australia the TGA (Therapeutic Goods Administration) tests the SPF of sunscreens before they are converted into the spray versions.
What SPF Should I use on my face?
There need be no difference between SPF ratings applied to the face and applied to the body, as long as it is adequate protection (we recommend SPF30).
There are however, two main differences between applying sunscreen to the face and the body.
The first is that the skin on the face is far more sensitive than the body, meaning you should choose the sunscreen you apply more carefully. Hypoallergenic sunscreens are much better for this and you can often find SPF that is a moisturiser as well, designed for daily use.
The second is that your face normally receives much more exposure to UVA radiation than the rest of your body. Ensuring you wear a suitable broad spectrum sunscreen daily is therefore important to prevent aging of the skin on the face.
SPF values are important, but they need to be read with an understanding of what they mean, otherwise they can cause more harm than good.
Most important is that you choose broad spectrum sun protection, of at least SPF30.
This is why all Soléo Organics sunscreens are broad spectrum, SPF30, providing equal protection from both UVA and UVB rays. See our sunscreens and the rest of their benefits here.
¹ Sunscreen use and duration of sun exposure: a double-blind, randomized trial: https://pubmed.ncbi.nlm.nih.gov/10433619/
² The relation between sun protection factor and amount of sunscreen applied in vivo: https://pubmed.ncbi.nlm.nih.gov/17493070/
³ Daily Use of a Facial Broad Spectrum Sunscreen Over One-Year Significantly Improves Clinical Evaluation of Photoaging: https://pubmed.ncbi.nlm.nih.gov/27749441/
⁴ Sunscreen and prevention of skin aging: a randomized trial: https://pubmed.ncbi.nlm.nih.gov/23732711/
⁵ Testing and Evaluating Aerosol Sunscreens: https://www.arpansa.gov.au/sites/default/files/aerosol_sunscreen_report_final.pdf