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Are we just too stupid to appreciate that sunscreens have limits?

January 24, 2018

OK so yes, I have gone for a rather ‘gotcha’ headline this time around but seriously people, this issue is serious.

Sunscreens have been in the news a lot just lately and not in a good way.  Several people have been burned, some very badly and tempers have become frayed as these unwitting customers question whether brand owners are just ripping people off, being deceptive in their marketing, not fulfilling their duties or are just ignorant to their products failings.  Whether any of this is true or not is looking likely to be a matter for the courts but my question today revolves more around personal responsibility:

‘Ask not what your sunscreen can do for you, but what you can do for your sunscreen’.

So are we just too stupid to appreciate that sunscreens have limits?

Now before you start throwing things at the screen and shouting obscenities I have to admit that I sympathise with the plight of the general public but being sympathetic and mumsy doesn’t seem to get the heart racing and the habits changing so I’ll just continue with this thought for a bit longer.

Today it wasn’t that hot for a summer’s day in Australia.  I think we topped out at 34C which, while muggy (due to the humidity) didn’t feel as bad as the 42C we had a few days before or the 39C on Monday and it was a bit cloudy at times so one might be forgiven for thinking that today might have been a ‘sunscreen optional’ sort of day in my neck of the woods.

However, a quick check of my Willyweather app shows me that the UV rating for today was off its chops as seen below:

There  is a very good explanation of UV index on Wikipedia if you want to know more, what interested me most was that the original scale went from 0-10 but these days with ozone depletion it’s not uncommon to see readings of up to 16 which is insane!  This PDF is also quite interesting from the USA EPA. 

In a nutshell the UV (Ultra Violet) index gives you an idea of how powerful the sun rays are at any particular time on any particular day.  Everybody tolerates the sun differently and even the same person can have days when their UV tolerance is a bit higher or lower than normal based on what they have been eating and drinking.

The UV index fluctuates across the day and there can be pockets of outdoor space that would read lower UV readings and spaces that would read higher.  Some surfaces reflect the UV rays back to you, intensifying them like a mirror –  snow is one such surface reflecting back around 80% of the rays and that’s why many people come back burned from their ski trip.  In comparison sand reflects back around 15% and water around 10%.   Higher altitudes will read higher UV ratings than lower, trees will prevent some of the UV from reaching you as will other types of shade or sitting on a surface that is non-reflective such as grass.

The UV index colour codes the zones from green to purple to show the risk levels based on an average person. On extreme UV days, at readings of 11 or more the advice is to actually avoid the sun altogether.  If that advice was heeded today, people in my area of the Blue Mountains should have been indoors between 11.30am and 2.30pm but of course people did go out today – some because they had to and others because they just didn’t think about the sun as they weren’t going to be sun baking.   But what happens when you want and need protection?

What can a sunscreen do?

Sunscreen reduces the amount of UV energy that reaches the skin which, in turn, takes some pressure off your own inbuilt UV protection system (Melanin etc).  We probably all know that but we don’t necessarily think through what that really means in a world that gives us varying levels of UV.

We might have an idea that our skin usually burns in about 10 minutes if un-protected so if we use an SPF 30 well we should be able to stay in the sun for 30 longer – 300 minutes or 5 hours – massive!

Only that calculation won’t be accurate if the UV index is extreme as solar simulators don’t use an extreme calibration point.

The solar simulators used by laboratories to come up with SPF data are calibrated to one particular agreed set of circumstances, they have to be in order to rank one SPF rating against another.  Nature doesn’t work like that and can throw up a whole host of different conditions on the same day and even at the same time of the day but in different locations.  In short, it gets very complicated.

I saw this table on a site called ‘The Ozone Hole” which gives some idea of how the UV index might impact burn times. I am not sure it is the best tool to use but it is better than nothing. Basically the higher the UV index, the shorter the time you will be protected by your SPF product. 

Rather than thinking about absolute time I’d look at this as a relationship thing as burning in less than 15 minutes is something of a life long dream for me, I can burn in less than 10!

I’d basically look at this and say that under extreme conditions (say UV 10) at mid day my SPF 30 will act like an SPF 15 if I apply it well.   I’d also assume that if the UV index was 12 or over I might only achieve 1/4 of the stated SPF IF I applied it well.  Remember that sunscreens are not sun blocks, some energy gets through and eventually I will burn, it’s just a matter of time (and UV dose).

Now this might not be accurate but it is a reasonable guesstimate based on the information I have here and if it were true then I could literally fry after only being in the sun for half an hour on a day like today in spite of slathering on the SPF 30.

So, in answer to my question ‘Are we just too stupid to appreciate that sunscreens have limits’ I’d say no we are not too stupid but we are probably not paying enough attention to the fact that their power is relative rather than absolute. 

The science behind sunscreens is complicated and it is very harsh to expect the public to understand and plan for the variability in the UV index, their activity level and the environment they are hanging in.   So, I think it is less of a case of us being stupid and more of a case of us not really being equip to live with such high UV indexes as standard.

Maybe we should all just stay inside and read between 11-2pm on these high UV intensity summer days!

For me the bottom line is that we need to start paying attention to UV ratings and thinking about the activities and environment we are going to be in each day, especially  for those of us with very fair skin but with the ozone hole nobody is immune from the burn here in Australia!  We do need to seriously consider how we spend those long summer days as it does look like there are parts of the day where no amount of slip, slop, slapping will get us through.

Basically SPF figures work under ‘normal’ sunlight intensity but where the UV levels are off the scale (old limit was 10 remember) we need to adjust our expectations down to more realistic levels.


PS: This is a particularly Australian / New Zealand problem, UV intensity varies around the world so please check your own environment before retreating indoors forever.

PPS: I found this article from 2010 on Solar Simulator variance very interesting.  Sunscreen SPF’s are relative to the UV spectra they were tested under and when that differs significantly from reality on any given day, the gap can mean a difference in real-time protection, maybe up to 50% less in some cases.


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