Dr John – the Chemist
Every year we read or hear of complaints that certain sunscreens fail and most manufacturers experience at least one or two such complaints.
Are sunscreens regulated?
Sunscreens are regulated as therapeutic goods in Australia and as such must be entered on the Australian Register of Therapeutic Goods (ARTG). The Therapeutic Goods Administration (TGA) ensure that all sunscreens have been tested to the Australian Standard before they are presented for sale. The Standard sets out methods and specifications to ensure that the product meets its label claim.
How are they tested and what does SPF mean?
Essentially each sunscreen is tested in the following manner. Firstly, ultraviolet light is applied to 10 test subjects of 3 different skin types until the first sign of reddening occurs, this is called the Minimum Erythemal Dose or MED. The sunscreen is then applied at the recommended rate and the UV light is applied again until the first sign of skin reddening occurs. The ratio of time in minutes from protected skin to unprotected skin is the Sun Protection Factor or SPF. Therefore, if it takes 10 minutes to make unprotected skin red then an SPF50 product, properly applied, would offer 500 minutes protection before the skin started to redden.
Chemical or mineral?
Recent research conducted in Hawaii has shown that some chemical sunscreen actives are responsible for coral damage. There has been a large trend away from chemical sunscreen actives as a result. Chemical actives must appear on labels and are usually quantified. These actives work by converting incident UV light into heat and are collectively known as solar absorbers. The most common being;
- Octyl salicylate
The move away for solar absorber has seen an equal sales rise in mineral sunscreen actives. The main contenders are;
- Zinc oxide
- Titanium dioxide
Mineral sunscreens work differently in as much as they reflect scatter incident UV light. The chemical or mineral options are regulated by the same mechanism, so each must demonstrate sufficient efficacy to protect against sunburn and UV damage.
Nano or non-nano?
Nano particles have been a contentious issue for a few years. Generally, a cautious approach is recommended by most scientists especially for inhaled particles. Many health authorities have reviewed the use of nano zinc oxide for use in sunscreens. They have almost universally decided that they are safe and effective for sunscreen use. Unfortunately those that would set out to bring some ingredients into disrepute have unnecessarily caused a decline in demand. Micronised zinc oxide is the preferred particle size despite the downside of more “ghosting” on the skin.
Can a product claim to be nano free?
In any powder there are particles of varying sizes and particles below 100nm of nano occur in small parentages. For this reason a product should not be claiming to be nano free or non-nano.
If sunscreens are heavily regulated why do they sometimes fail to work?
So why do some sunscreens appear not to work? Apparent sunscreen failure happens couple of times a season for every sunscreen brand. Wild Child Laboratories manufactures over 100 tonnes of sunscreen per year for various brands. During that time, we typically we experience about 2 or 3 complaints relating to product efficacy on average. When we re-test the product we have always found that it met with its release specification. After several interviews with complainants, we determined that product failure seems to be always linked to insufficient use or allergy.
How do we get application rate so wrong?
Our skin constantly changes tone during the course of a year and is much more sensitive to ultraviolet light in the springtime than it would in mid-summer or autumn. This is largely due to the loss of the pigment melanin during the winter months. As our exposure to ultraviolet light progresses melanin levels in our skin increase. As a consequence, we become more and more immune to low to moderate UV levels. It is therefore quite common for most of us to be accidently sunburnt in the early summer months because we are used to not taking precautions when exposed to winter sunshine with low UV levels.
How does sunburn happen even though we apply sunscreen?
We typically go out into the sun in the spring and only apply sunscreen once we start to feel warm or hot. Unfortunately, on a high UV index day this is too late to prevent burning because the damage (erythema) has already occurred. Therefore, manufacturers are required by TGA to place instructions on sunscreen to apply 20 minutes before exposure. In addition, the amount of sunscreen applied varies dramatically between individual users and is the primary cause of sunscreen failure. With zinc oxide type sunscreens, we have a habit of rubbing the product in until we can’t see any whiteness.
Unfortunately, this is not enough sunscreen to give maximum benefit, the scientifically determined application rate for sunscreens is 2mg per square cm, this may not sound a lot but is equivalent to about 20g or 1/5 of a tube of product on a 5-year-old. Sunscreen sprays, roll on and stick products are less likely to be applied correctly, once again because of our interpretation of how much is enough. The third important aspect of sunscreen protection is re-application. The Australian standard calls for immersion tests that determine the water resistance of sunscreens, unfortunately the standard does not allow for towelling off or loss by abrasion. This means that the re-application times should be more frequent if a child is towelled off after swimming. We usually recommend re-application after each swimming session.
What part does skin allergy play?
Finally, and somewhat rarely, some individuals have an immune response to sunlight called solar urticaria, this can manifest itself in many ways but typically shows up as a reddening of the skin. The immune response is sometimes stimulated in some individuals by the chemical compounds in sunscreens, usually the preservatives. This is not actually sunburn but is the skins immune response to ultraviolet light exposure. In a lot of cases, it is typified by the fact that the skin is itchy rather than sunburnt and may sometimes have associated wheals or welts. Frustratingly, photosensitivity changes with time and amount of exposure so an apparent severe reaction now may not appear in a couple of months’ time or when a different product is used. Obviously, the end user would quickly conclude that product “x” doesn’t work while product “y” is fine. This observation is incorrect but understandingly one easy to arrive at.