Sunscreen, Application, Product comparisons, SPF
I’ve always had reservations about the use of aerosol* based sunscreens since I had heard reports of people accidentally setting themselves on fire in the United States. Having seen an increased number of product performance complaints about aerosol based sunscreens, I had serious doubts about the ability for these products to achieve the claimed sun protection factor (SPF) and ability to prevent sunburn.
I have investigated the potential dangers of aerosol sunscreen using basic research and laboratory testing using an aerosol sunscreen that is currently on the market. While I don’t disagree with the convenience of the product and that it could encourage people to use sunscreen when they otherwise may not have and that there is a consumer demand for such products, the investigation show that my reservations were very much warranted. As I will now explain, while the products appear easy to use, they must be used with caution, so much so, that consumer should consider whether the ‘convenience’ of aerosol application is worth the risk associated with their use.
Flammability
As previously noted, there have been instances in the United States where people have caught on fire after applying aerosol based sunscreen products, causing serious burns. This is not surprising given the flammability of the Hydrocarbon (Butane) propellant/gas and Ethanol solvents used in these products. The dangers are clearly stated on pack in the form of a flammable goods placard and other written warnings on the dangerous and how not to use the product.
The risk remains that applying sunscreens around BBQ’s, people who are smoking and other sources of spark or naked flame can cause the product and persons wearing the product to catch on fire . The irony being while in the process of attempting to reduce the risk of sunburn we have increased the risk of an actual burn to our skin.
Asphyxiation
Asphyxiation refers to breathing in a gas/propellant with a reduced amount of oxygen in the air which lowers oxygen concentration in the blood stream, potentially leading to unconsciousness. Again, despite warnings on packs advising that sunscreens must be applied in a well-ventilated area, there is a risk that the user will apply the sunscreen in an enclosed space, potentially leading to asphyxiation and unconsciousness.
Explosion
No sunscreen should be left in a car which is in the sun (especially during summer) or exposed to direct sunlight or left anywhere where it may be exposed to temperatures over 30degC, as elevated temperatures will cause a degradation of the product and impact the claimed performance. The need to avoid high temperatures is even more important for aerosol sunscreens which are pressurized containers, as heat will cause the pressure within the can to increase and there is a risk of the aerosol explodin.
SPF testing and certification
The sun protection factor (SPF) of aerosol sunscreens aren’t tested and certified in the laboratory using the same application methods used for regular sunscreens and by us as consumers. The reason for this is one of practicality; the propellant/gas in the aerosol makes following the standard test method virtually impossible as the amount dispensed and applied to the skin cannot be accurately measured as the packaged product in its original form is so volatile, because of this, an alternative method is used. During laboratory testing, the volatile propellant/gas is removed from the aerosol can before testing starts, leaving only the liquid inside, this liquid is then tested in the same way as with a regular sunscreen. The propellant/gas accounts for around 40% of the contents of the aerosol, meaning 40% of product is lost during the application process with only 60% of the contents having the ability to reach our skin where it can provide the necessary protection.
The above is not a flaw in the test used to certify the SPF, however it does impact the products ability to achieve its stated SPF as a result of needing more sunscreen to be applied than would be thought necessary.
Following on from the above, when tested in the laboratory, the product is physically applied to human skin and ‘rubbed’ in, however the directions and the aerosol packaging require that the product be sprayed directly onto your skin. The spray application can affect the quality of the sunscreen layer that is formed and subsequently the quality of protection. The image below shows a close-up photo of the sunscreen after application using the sunscreen liquid rubbed on vs directly sprayed on from the aerosol sunscreen packaging, you can clearly see the difference in texture of the sunscreen and these differences could affect the quality of protection:
Loss during application
Because of the gas/propellant and the fine mist released during use, the amount of product that comes out of a can of aerosol sunscreen is not the same as what ends up on our skin. Most brands recommend spraying the product 10-15cm away from our skin and laboratory testing under ideal conditions (i.e. indoors – well ventilated area, no wind) using these guidelines found that only around 40% of the amount dispensed from the pack actually ends up on the skin. The loss of 60% of the product in application is now 20% above the gas/propellant loss outlined earlier where it was estimated 60% would reach the skin this additional loss is attributable to ‘overspray’. This loss in application would be worse if there were a breeze, if the area of application was small (such as a child’s arms and legs) or was being applied from a distance greater than the recommended 10-15cm.
Combining the amount of gas/propellant lost during application and the overspray, the total loss during application is significant at 60% of the amount in the aerosol, with only 40% reaching the skin where it can provide the necessary protection.
Change in pressure and amount applied
Over the life of an aerosol as the product is used, the amount of product/propellant in the can becomes less and this reduces the pressure within the aerosol. The pressure in the aerosol is responsible for the product being released during application, less pressure in the aerosol can results in the amount of product dispensed over a particular time becoming less. Some research found that the product would need to be sprayed 45% longer as the can approaches being empty to allow the same amount of product out of the can. Whilst it is reasonable for a user to take additional time to ensure proper application, given the sunscreen is transparent, it would be difficult for a person to understand that this would be necessary to ensure they achieve the claimed level of sunscreen protection (SPF).
Similarly, ambient temperatures can impact the aerosol pressure. Cooler temperatures reduce the pressure and the application amount, whilst warmer temperatures will increase the pressure and increase the application amount.
Understanding the application properties
To achieve the claimed SPF for regular sunscreen (non-aerosol), the average adult requires approximately 36g of product when being applied over the entire body, for the golfers out there; this is roughly the size of a golf ball in terms of volume, for the cooks, its 1.5-2 tablespoons. It is difficult enough for a person using a regular sunscreen lotion to understand what this means when sunscreens aren’t sold in golf balls and we don’t carry a set of measuring spoons. It’s even more difficult to comprehend when using an aerosol sunscreen and the dispensed product which is bordering on invisible!
I decided to try applying the sunscreen for myself to see how much sunscreen reaches my skin, weighing the aerosol before and after application, timing the application to get an idea of how long the process takes and applying what ‘felt’ appropriate. I spent a total of 2 minutes applying the aerosol sunscreen and calculated that roughly 35g of product was dispensed from the aerosol. Allowing for the gas/propellant and over-spray, I estimated 40% of the 35g would have reached my skin, meaning 14g of sunscreen reached my skin, which is just 35-40% of what I should be wearing to achieve the claimed level of sun protection (SPF)
So, should I use aerosol sunscreen?
Using the diagram above as a guide, an adult who would normally require 36g of product would need 90g from an aerosol sunscreen to obtain the 36g of product. The 90g required makes ~4.5 minutes of continuous spraying to achieve, 4.5 minutes spraying a flammable product which dramatically increases the likelihood of catching fire!
Below is the previous diagram showing the weight distribution during application to clarify.
This means that for the average adult applying sunscreen to their entire body, you should be getting only 2 applications from the average 175g can (2 applications x 90g = 180g, a fraction more than the 175g in the average aerosol).
Going back to my experiment where I applied 40% of the recommended amount of sunscreen onto the skin i.e. 14g of the 36g dispensed as a result of propellant/gas and over-spray, I calculated that the SPF50+ sunscreen (over 500 minutes of protection) was now only SPF5 (50 minutes of protection), less than 10% of the claimed protection.
The dramatic reduction in protection when combined with the increased risks of flammability and explosion, I know that I won’t be using aerosol based sunscreens, having said that however, aerosol sunscreens are safe to use when used correctly, so for those who prefer the convenience of using aerosols, please use this article as a guide to how best to achieve the most out of your favorite sunscreen and minimize the risk.
*Aerosol in the context of this article refers to aerosol spray/mist type packaging as distinct from other forms of aerosol, including bag-on-valve and bag-in-can where the propellant is separated from the product, as used for dispensing creams, lotions and gels which don’t have the same dangers with respect to flammability, asphyxiation, explosion, losses during application etc.
http://www.fda.gov/downloads/ForConsumers/ConsumerUpdates/UCM258910.pdf
Sunscreen, Product comparisons, SPF
SolarD sunscreen was introduced into the Australian market in late 2014, advertised as being a technologically advanced formula that permits the particular wavelengths of ultra-violet light that your body uses to naturally produce vitamin D. The concept for this product is new and no doubt of interest to consumers with the increasing concerns over their vitamin D levels and reports that regular sunscreens prevent vitamin D production. Without suggesting that people should avoid using SolarD, I do feel that it should be used with caution and appropriate consideration for their sunscreen needs, lifestyle and the recommendation of their doctor.
Importance of vitamin D
Vitamin D, as with all vitamins are essential to our health, vitamin D helps the absorbtion of minerals including; calcium, iron, magnesium, phosphate and zinc, all of which are critical to bone health. Being deficient in vitamin D can cause rickets, osteomalacia and osteoporosis and has been linked to cancer, various auto-immune, cardiovascular disease and mental health.
The recommended daily amount (RDA) of vitamin D for adults who do not have a vitamin D deficiency is 600IU, this is equivalent to 0.0000015g (15µg).
Sources of vitamin D
There are two types of vitamin D, D2 and D3; vitamin D2 is found in mushrooms and ‘fortified foods’ such as milk, margarine and breakfast cereals where the vitamins have been artificially added. Sources of vitamin D3 include foods such as salmon and other oily fish, eggs and milk in addition to fortified foods and vitamin D supplements, vitamin D is also produced through sun exposure.
Vitamin D3 is the most potent and effective type of vitamin D with sun exposure being the most efficient means of attaining our vitamin D3.
The most concentrated dietary source of vitamin D is found in wild salmon which has up to 1000IU of vitamin D3 in every 100g. Turns out that a salmon a day could keep the vitamin D deficiency away, unfortunately, eating salmon everyday is not great for a balanced diet, which is why sun exposure is important.
Vitamin D3 and sun exposure
Producing vitamin D3 through sun exposure is a complex reaction that occurs within our skin, requiring sun light to drive the reaction, specifically the wavelengths of light between 270 and 320nm. Visible light are those wavelengths between 390-700nm, as the wavelengths of light required to produce vitamin D3 are below those of the visible, they are ‘ultra-violet’ (UV) wavelengths which we can call UV light.
The amount of vitamin D3 produced when exposing ourselves to sun light will vary considerably with the amount of exposed skin, age, height, skin color, time of day, season, longitude and altitude, from as little as a few minutes in summer, to a few hours in winter. Interestingly, the amount of vitamin D generated in the skin is limited, to the point where longer exposure to sun light will not necessarily increase our vitamin D levels, unlike the risk of skin damage and skin cancer which will increase the longer we spend in the sun.
Causes of sunburn and the vitamin D paradox
Ultra-violet B (UVB) light refers to those wavelengths of light between 280 and 315nm, Ultra-violet A (UVA) are those wavelengths between 315 and 390nm. The UVB wavelengths are most responsible for causing sunburn, but are also responsible for causing skin cancer and other sun damage, particularly premature ageing such as wrinkles and sun spots. The method used to test the sun protection factor (SPF) of a product uses sunburn as the endpoint to determine whether the product is providing protection simply because the sunburn is an indicator of sun damage that is (close to) immediately visible and easily measured.
You may now note that the wavelengths of light that are required to produce of vitamin D3 detailed above are the same as those that cause sunburn. A sunscreen that is aimed to prevent sunburn and that is promoted to permit the particular UVB light that your body uses to naturally produce vitamin D3 should be physically impossible.
A look at how Solar D works
The UV absorbtion spectrum of SolarD SPF50 sunscreen in comparison to a regular SPF50+ Sunscreen (below) shows SolarD absorbs less light in the UVB (280 – 315nm) region than a standard sunscreen, which goes to justify the claim that SolarD permits the particular UVB light that produce vitamin D3, but doesn’t necessarily support the SPF50 claim.
How does SolarD make sun protection claims if there isn’t enough UVB absorbtion to prevent sunburn?
Before I go into any further detail and to place the remainder of this article in context, I must highlight that I am not aware of SolarD’s technology or formulation so I do not know with any certainty how SolarD achieves their claims. Being involved in the development of sunscreens (as I am) and having been aware of the health issues surrounding vitamin D, I had already considered ways that a sunscreen can promote vitamin D production and protect against sunburn, they are unusual and in my mind, not necessarily in the consumers best interest.
Sunburn is only one symptom of sun exposure, it is the one we readily relate to as we see and feel it so soon after we have been in the sun, other symptoms include skin cancer and premature ageing such as wrinkles and sun spots. We often treat sunburn using after sun products containing anti-inflammatory ingredients such as aloe vera and green tea and also anaesthetics like lidocaine, but these products won’t undo the damage that has already been caused, only reduce the redness/pain we can see and feel.
A sunscreen could, in theory, have a high sun protection factor (SPF) without the need for the product to absorb a lot of UV light by treating the visible symptoms of sun exposure we know as sunburn. A product such as this would be reliant on those same anti-inflammatory ingredients used in after sun products to compensate for a reduction in UV absorbance relative to that of a normal sunscreen. The issue here is that by failing to absorb as much UV light, more damaging UV light will be allowed to pass through to the skin where damage will occur despite the sunburn having been masked by the ant-inflammatory action. We could liken this to spraining your ankle whilst on pain and anti-inflammatory medication, the damage was done, the ankle is now weak and unstable, we just can’t feel it and in no way was the damage prevented.
I am not suggesting that this is how SolarD functions, without seeing the product technology in its entirety; this is only my theory on how the product may perform and something worth being mindful of.
Vitamin D production vs sun protection
The primary purpose for any sunscreen is to minimize sun damage by absorbing the UV light and reducing the risks of sunburn, skin cancer and premature ageing when we’re out in the sun. Realizing that sunscreens have an obvious potential to alter the way vitamin D3 is formed and influence vitamin D deficiency and related diseases, we need to instill a balanced approach so that we get enough sun exposure to allow vitamin D production, but not so much as to cause sun damage.
While wearing a regular SPF50+ sunscreen in summer will slow the formation of vitamin D3, the small amount of UV light which does pass through over the period of a few hours will generate the same amount of vitamin D3 as spending a few minutes without sunscreen with the added benefit of their being less risk of damaging the skin and there have been studies that show this to be the case.
We should all use sunscreen whenever there is a risk of sunburn, if there is no risk of sunburn, there is no need to wear sunscreen, if in doubt though, your best to have sunscreen on. If you’re going to be outdoors outside peak sunburn times (early morning or late afternoon) or only for very short periods during the day, there is no need to apply sunscreen, by doing so, our bodies will be produce vitamin D3. For those who have concerns relating to premature ageing such as wrinkles and sun spints and prefer to wear sunscreen at all times, then SolarD may be a good option to minimize damage without inhibiting vitamin D too much, a lower SPF sunscreen would however have a similar effect.
For those who are planning on spending a lot of time in the sun, especially at the beach, pool or playing sport, your best to wear a 4 hour water resistant SPF50+ sunscreen for maximum protection, remembering the sunscreen will allow vitamin D3 to be formed. I stress this point because SolarD, being a 2 hour water resistant SPF50 sunscreen has 15-20% less SPF and half the water resistance of a 4 hour water resistant SPF50+ which is not going to provide the best protection.
To buy SolarD or not to buy SolarD
I don’t want to discourage people from using SolarD, it’s an interesting concept that will have a place on the market, however it does complicate the decision making process, particularly for those who believe their existing sunscreen is somehow less effective in terms of allowing vitamin D production to occur.
If you haven’t been diagnosed with a vitamin D deficiency, then your current lifestyle and existing sunscreen habits are working for you, there is no need for a product like SolarD. For those who have been diagnosed with a vitamin D deficiency, your doctor would offer the best solution with consideration for minor lifestyle changes to get more sun, using vitamin D supplements and perhaps recommend SolarD.
References
- Olds, 2010; Elucidating the Links Between UV Radiation and Vitamin D Synthesis; Using an In Vitro Model, Queensland University of Technology.
Sunscreen, SPF
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’:
