When choosing sunscreen, many 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, did you know that SPF is considered unreliable for measuring a sunscreen's effectiveness.
Read on to learn what SPF means, what it measures, what it doesn’t measure, what various authorities say, and much more.
What's the Meaning of SPF?
- Acronym for 'Sun Protection Factor'
- Measures Protection From Sunburn
SPF means Sun Protection Factor.
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 measure of sun protection.
Officially it's a formula for determining the fraction of Ultra Violet B (UVB) rays that will reach the skin. Practically it's just a measure of how well a sunscreen protects the skin from being burnt.
You can read it as how many times longer, you can stay out in the sun, than if hadn't put on sunscreen.
Higher SPF's Mean More Time without Being Burnt
SPF30 means 30 times longer in the sun without being burnt, SPF15 means 15 times longer.
For the more technical folks, that's because, 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.
How it's Calculated
The SPF is calculated using human volunteers in a laboratory. The time it takes for an untanned piece of skin to be burned with and without sunscreen is measured. The bigger the difference, the higher the SPF of the sunscreen. For example, if it takes 30 seconds for the skin to burn slightly without the sunscreen, and 900 seconds for it to burn with the sunscreen, 900 divided by 30 gives us an SPF of 30.
Sometimes the SPF also has a plus after it, I.e. SPF30+. The plus indicates that the SPF is higher than the number.
All pretty simple right? So why would it not be an accurate measure?
What SPF Doesn’t Mean
A higher SPF does not mean a lower application frequency, nor does it mean complete protection from the sun.
SPF just means protection from being burnt.
Unfortunately people frequently assume that a high SPF effects these things, let's have a closer look.
How Long it Lasts
- SPF has no impact on Reapplication
It's very important to realise SPF 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 directed with the same frequency as even the lowest SPF sunscreen.
In fact on chemical sunscreens, the application frequency is determined by how long it takes for the skin to fully absorb the chemicals.
With mineral sunscreens, it's more the amount of time it takes for sweat, movement, and clothing to remove the sunscreen.
For most sunscreens, you need to reapply every two hours.
- SPF has no impact on protection from UVA Radiation
- UVA is the Primary Cause of Skin Aging
- It Accounts for 95% of Sun's Rays
- It Travels through Windows/Clouds
SPF ratings have no impact on protection from UV-A radiation, in fact, often higher SPF sunscreens provide less UVA protection.
When sunscreen was originally developed very little was known about Ultra Violet A radiation (UVA). SPF was developed to only measure against UVB radiation, the rays that burn the skin.
Since then we have learned a great deal about UVA rays, radiation that penetrates much deeper and is the primary cause of skin aging, wrinkles, and certain types on cancer. Accounting for 95% of the sun's ultraviolet radiation, it's made worse by the fact that UVA rays travel through clouds and even windows, which would stop UVB rays.
This is why it's so important to wear sunscreen, even on a cloudy day.
Protection from UVA radiation has become a foundational part of most beauty routines, and a broad-spectrum sunscreen (one that protects from both UVA and UVB rays) has become the single most important cosmetic item.
One of the primary issues with SPF is that it doesn’t measure protection against UVA radiation at all. People often opt for a higher SPF, and even if they were to pick a broad-spectrum sunscreen, they often end up with lower UVA protection.
Most of the higher SPF formulas have been adjusted to offer the maximum UVB protection at the cost of the UVA protection.
What's Wrong With SPF50?
Did you know the Cancer Council in Australia recommends SPF30 or above, not SPF50?
SPF50 sounds almost double SPF30, but that simply isn't accurate when looking at SPF calculations.
Understanding SPF Calculations
- SPF can be Converted to a Percentage of Protection
- SPF 30 has 96.7% Protection, SPF 50 has 98%
- There's a 1.3% difference between SPF30 & SPF50
For our more technical readers, here is the maths, If you'd rather just have the answer then skip this paragraph.
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 of the UV rays reach the skin. 1 divided by 50 is 0.02. Converting that to a percentage by multiplying by 100 is 2%.
2% Reaching the skin means that SPF50 prevents 98% of the UVB radiation from reaching the skin. If we run the numbers for SPF30. SPF30 prevents 96.7% of the UVB radiation from reaching the skin.
Why a Higher SPF is not necessarily better
- The Danger of High SPF Products is the Perception
- Many Countries Capped the Legal SPF to 50+
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.
What the World Health Organisation Says
- SPF15 or Above is Recommended
- Proper use is far more important than SPF
The World Health Organisation recommends a broad spectrum sunscreen, of SPF15 (meaning 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. He indicates that people using SPF50, were far less careful to reapply or even apply properly.
Simply put the World Health Organisations view is that you should use a broad spectrum SPF15 sunscreen or above, and apply it properly. Proper use, and reapplication is far more important than the SPF value of the sunscreen.
What the Health Authorities Decided
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.
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.
Does How Much Sunscreen I Put On Impact the Rating?
- It's Very Important to Apply the Correct Amount
- Half the amount of SPF 50 gives SPF 7 Protection
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.
I.e. applying half the correct amount of a SPF50, only gives you SPF7 protection.
That is a big difference. Applying the correct amount is far more important than most people realise.
Applying the Correct Amount
- Generally 1 Teaspoon per Body Area
There is a general rule to applying the correct amount of sunscreen, although it should never override the instructions on the tube.
As a general rule experts recommend 2mg per cm² of skin, or more simply this usually equates to about a teaspoon per area covered. For example, a teaspoon per arm, or a teaspoon for your neck, face and ears.
What about SPF sprays (Spray on Sunscreen)?
- Always ensure ample quantity sprayed
While on this point we should talk about spray based SPF, are spray on sunscreens effective?
A study done by the Queensland University of Technology⁵ 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.
Remembering how important application amount is to achieve the SPF rating of protection, it's obvious that it's very important you follow the directions on the label to achieve the desired SPF.
What SPF Should I Use?
- We Recommend SPF30
- Anything SPF15 or Higher is Suitable for Most People
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.
The Most Important Takeaway
- Reapply Sunscreen Regularly
- Choose Broad Spectrum Sunscreen
The most important thing to remember from this article is that the SPF is not nearly as important, as making sure you are protected from UVA and UVB radiation every day. Just putting on sunscreen is not enough.
Ensure it's a broad-spectrum sunscreen and that you reapply frequently enough (as determined by the label).
It's also extremely important that you apply enough in the first place. Applying less than the recommended amount drastically reduces the amount of protection you receive.
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.
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 an organic face sunscreen 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.
What does UPF mean?
UPF stands for Ultraviolet Protection Factor, and it means how much UVA and UVB radiation is blocked by a fabric. The UPF ratings are generally used on outdoor clothing, and the biggest distinguishment between UPF ratings and SPF ratings are the fact that UPF ratings measure against both UVA and UVB radiation, while SPF only measures against UVB radiation. Besides this fact, the measurement is very similar to SPF, with a UPF 30 shirt allowing only 1/30th of the UV radiation to reach the skin, in the same way an SPF30 sunscreen allows only 1/30th to reach the skin.
What do PA ratings mean?
The PA rating system was developed in Japan to represent protection from ultra violet a radiation (UVA). The PA system goes from PA+ to PA++++ with PA+ meaning light UVA protection and PA++++ meaning extremely high UVA protection. While the PA system seems like a great step in the right direction, there are some global concerns around it.
The PA system only measures what is referred to as persistent pigment darkening, or in other words the skin tanning under the UVA radiation. The problem with this is the inconsistency between people tested on. This has brought some concerns about its reliability.
What is the UV Index?
The UV Index is a measurement of the amount of Ultra Violet radiation being output by the sun. This is normally measured using detectors in cities, that respond to the ultraviolet radiation similarly to our skin.
UV index charts normally give a UV value for the day that estimates what the maximum daily level of Ultraviolet radiation will be.
You can use the UV index to estimate just how important it is for you to take protective measures against the sun. The readings are generally categorised like the following.
Low Rating (UV 1 - 2)
Moderate (UV 3 - 5)
High (UV 6 - 7)
Very High (UV 8 - 10)
Extreme (UV 11+)
You can use the below websites for UV ratings for your locataion.
EPA's UV Index
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 organic sunscreens are broad spectrum, SPF30, providing equal protection from both UVA and UVB rays.
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