Tag Archives: SPF50+

More is more, how much sunscreen is enough?

Despite high SPF50+ sunscreens on the market that are capable of providing hours of protection from sun damage, it’s an unfortunate reality that people continue to become sun burnt while wearing sunscreen. The reasons why we’re still getting sun burnt are simple – we aren’t applying enough sunscreen to properly protect ourselves. Having done some investigation, I was incredibly surprised exactly how important applying the recommended amount of sunscreen is and that applying anything less gives an almost catastrophic reduction in protection.


Sunscreen testing and certification

Before going into detail, it’s worth noting that the sun protection factor (SPF) claimed on packaging have been certified in a laboratory under very detailed conditions relating to the amount of product applied to a surface area (for the technical people, its 2mg/cm-2). For your sunscreen to achieve the claimed SPF, it must be applied in the same manner and for the average adult, this means approximately 36grams (roughly 36mL) for a full body application. For the golfers out there; 36mL is roughly the size of a golf ball in terms of volume, for the chefs/cooks, its 1.5-2 Tablespoons. For those whom are above average in terms of weight or height, they’ll need to use more sunscreen and for those smaller than average (including children) less can be used.

Case Study

To use an example of how poorly this is communicated to consumers, I recently received a customer complaint where an individual believed that their SPF50+ sunscreen was faulty as the family were  sun burnt after using the product.  A detailed investigation found that product was not faulty, leaving consumer misuse as the likely cause.

To set the scene, a husband, wife and three children were holidaying in Queensland, Australia and spent the day at a water park between the hours of 9am to 5pm, using a SPF50+ sunscreen. The questionnaire completed by the parents suggests they followed the product directions and re-applied every 2 hours. An SPF50+ sunscreen should provide 10 hours of sun burn protection if used correctly, more than enough protection for the 8 hours they enjoyed the sun. The reason the family became sun burnt was revealed in the answer to the question “How much sunscreen was used?” the answer;  “half a 100mL bottle”, interestingly  the amount was also described by the consumer as a “liberal” application. Some fairly straightforward math here shows that 50mL used on 5 people would require ~10mL per person all day, with 4 applications, that’s ~2mL each application, does that sound like enough when we’re supposed to being using ~36mL every 2 hours?


Some more detailed math, taking into account the surface area of average  adults and children show that the family used, on average roughly 1/8th of the 36mL used to substantiate the SPF50+ claim. If we  assume that having used 1/8th of the recommended amount, the protection would be 1/8th of the labelled SPF, this equates to an SPF of 7.5 (75 minutes) – insufficient protection for the 8 hours they were out in the sun. The reality however is considerably worse as physics is a cruel mistress, and doing something as simple as halving the quantity applied does more than just halve the performance because absorbance is what is referred to as ‘logarithmic’, bear with me as I attempt to explain.

The quantity of UV light that passes through a sunscreen diminishes more and more as it passes through, a visual explanation is provided below using a SPF 3 (offering 30 minutes of protection) sunscreen absorbing 66% of light and applied in 4 layers to create protection equal to that of a SPF75 sunscreen (offering 750 minutes of protection), 25x more protection than a single layer:


So what’s happening in the above diagram you may ask? The first layer absorbs 66% of the light, transmitting 34%, at this point we focus on what is being transmitted to illustrate, if the second layer transmits 34% of the 34% transmitted by the first layer, then the second layer transmits 11.56% (34% x 34%), the third layer transmits 34% of the 11.56% (11.56% x 34% = 3.93%) and so on and so forth.

The same works in reverse for a sunscreen which has been incorrectly applied as follows:


The above shows that using 1/4 (25%) of the recommended amount of SPF50+ sunscreen (offering 600 minutes of protection) creates protection equivalent to an SPF3 sunscreen (offering 30 minutes of protection). Going back to the original complaint where the consumer was found to have used 1/8th of the recommended amount, the equivalent protection is in fact less than SPF2, it was almost not worth the effort or expense applying any sunscreen!

The below graph may also help to explain the relationship between SPF and applied amount:


There have been a number of studies performed demonstrating how little sunscreen we as consumers apply and that sunscreen performance claimed is rarely achieved. I suggest that the underlying fault lies in the standards used to substantiate SPF where there is a huge difference between the amounts used to measure SPF in the laboratory and that typically used when we’re at the pool, beach or playing sport.

What does it all mean?

It is not necessarily reasonable to expect consumers to fully appreciate the amount we should be applying, we apply what feels right and what feels right is rarely the recommended amount! Logic suggests that the standards used to certify sunscreen should be updated to incorporate an amount that reflects what we use, or at least something more in-line with what we use, such that the claimed SPF is similar to that which we can expect to achieve. Having said that, the implications are that SPF50+ as the maximum claimable SPF isn’t likely to be reduced to account for a lower use amount so it really is up to the sunscreen industry to formulate product the encourages the use of more sunscreen, in the meantime however, we as consumers must learn to apply sunscreen properly.

It is simply not enough just to be wearing ‘some’ sunscreen, particularly if your intention is to be out in the sun for long periods of time, you must apply ‘a lot’ of sunscreen. If we were to think of UV radiation as a bullet with the potential to kill you, sunscreen could be thought of as a bullet proof vest and wrapping ourselves in aluminum foil is not going to stop a bullet… How much sunscreen should you apply, the answer is quite simply ‘a lot’.

And don’t forget to re-apply frequently!

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MythBusting SPF50+ Sunscreens


With the introduction of SPF50+ sunscreens into Australia in late 2012, early 2013, there had been, and continues to be, a belief by some (including some fairly reputable organizations), that there is a negligible increase in protection as compared to previous generation SPF30+ sunscreens. Given SPF is the acronym for ‘Sun Protection Factor’, logic should prevail that 50+ provides considerably better protection than 30 and it is, twice as good in fact!

The articles that have been written dismissing SPF50+ will always raise a supposed minor change in protection by referring to a “1.3% increase in protection” which is an incorrect representation of a factual figure. There is a 1.3% increase, however the increase relates to the absorbance, where SPF30 sunscreen absorbs 96.67% of UVB radiation (and plenty of UVA also), whilst SPF50 sunscreen absorbs 98.00% of UVB radiation (SPF50+ actually absorbs over 98.33%). If we presume an SPF30 sunscreen was to provide 300 minutes of protection, an SPF50 sunscreen certainly does not offer a paltry additional 3.9 minutes in the sun (300 minutes multiplied by the supposed “1.3% increase in protection”).

Absorbance is a measure of a physical property of a sunscreen, a moment in time, the missing piece of the puzzle, the piece that is used in calculating the SPF of a sunscreen, is time. Attempting to measure protection by referencing absorbance alone is like trying to measure speed by referencing distance and not accounting for time, something that would have Galileo rolling in his grave.

What is more critical for a sunscreen in terms of protection is not what the sunscreen absorbs, but what is does not, this is referred to as transmission, the amount of UV radiation that is not absorbed and has passed through the sunscreen onto the skin where it can cause damage. If an SPF50+ sunscreen transmits 1.67% (100% – the 98.33% absorbed) and an SPF30+ sunscreen transmits 3.33%, it quickly becomes obvious that the SPF50+ is transmitting half the amount of UVB radiation through and absorbing 200% more UVB radiation, that 1.3% sounds like allot now!

If the average person burns in 10 minutes, the amount of time a person can spend in the sun before becoming sun burnt (and would be considered ‘protected’) can be determined using the following simple equation:

Time = 10 minutes / Transmission (%)

Now let’s apply that to some SPF values:

  • SPF0 – Not a valid SPF
  • SPF1 – 10 minutes (no protection, calculated on 100% transmission), realizing this is not an valid SPF from a product perspective, but our skins natural protection factor.
  • SPF2 – 20 minutes
  • SPF30 – 300 minutes
  • SPF50 – 500 minutes
  • SPF50+ – 600 minutes

Now in graph form:


Its worth keeping in mind that the above calculations assume the sunscreen is used appropriately, which it often isn’t and this is largely the reason why SPF50+ sunscreens are being made available, to account for improper use (I’ll discuss this more later, suffice to say, people are still getting sun burnt!).

Amanda at Realize Beauty offers a more visual explanation on her blog.

Some examples of websites and organisation promoting ‘The Myth’:

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