SPF: three letters that guard us from the sun

Summer is back with a bang and most of you are probably already daydreaming about holidays. Apart from cocktails by the beach, lounging around and swimming in the sea, most people are also probably thinking about getting a tan and are already preparing a whole bunch of different products to turn their skin into that of a bronze goddess. However, are they also thinking about the less “sunny” side of sunbathing and proper protection against harmful effects of UV radiation? Our dear associate, Lucija Božičević is here to remind you of the importance of high quality UV protection.

First let’s present the different types of ultraviolet (UV) radiation. There are three – UVA, UVB and UVC. UVA rays (wave length of 320-400 nm) penetrate into the deeper layers of the skin (the dermis) and are responsible for aging and non-acute long-term skin damage. Acute damage of the surface layers of the skin or burns are caused by UVB radiation (wave length of 290-320 nm). So aging is caused by UVA rays and burns are caused by UVB rays, and the initial letters of these two terms make it easy for you to remember which causes which. There is also UVC radiation but this type is rarely mentioned since it is successfully eliminated by the atmosphere and doesn’t reach the Earth.

As far as protection against sun rays is concerned, we all know that it’s expressed through protection factors or more popularly, SPF. But what is SPF really? To start, one must keep in mind that the protection factor describes only the ability of the product to protect against UVB rays. It is considered that a person with a completely normal skin type can last 10 to 20 minutes in the sun without getting sunburn. This timeframe may of course vary depending on numerous factors such as the location where you are sunbathing and the time of day. Let’s say you are able to spend 10 minutes in the sun without getting burned. If you use SPF30 then this number climbs to 300 minutes, meaning that the SPF number stands for how much times longer you can stay in the sun without burning in comparison to staying in the sun without protection. The general opinion is that SPF15 repels 93% of rays, SPF30 97%, and SPF50 98%. As you can see, the higher the SPF, the higher the protection. Another thing to note though: the higher the SPF, the smaller the difference in the protection it provides in comparison to the preceding, lower SPF factor.

You may be asking yourself if SPF refers only to UVB radiation how will you know if your product is also protecting you against UVA radiation. Products for which extensive laboratory research has proven that they also protect against UVA rays are classified as broad spectrum. At present, if you are using a product that is marked as broad spectrum it is considered that UVA protection is satisfactory, that is, that the two requirements defined by standardised methods have been satisfied. The first requirement is that the UVB:UVA protection ratio equals or is less than 2.5, and the second that the filters cover previously defined critical wave length values that pertain to both types of UV radiation. In Europe, the level of UVA protection is determined by using the in vitro method prescribed by COLIPA guidelines. Measurements are carried out by spectrophotometry and are standardised, reproducible and transferable from one laboratory to another. The acquired results are observed in correlation with in vivo results, which gives final information on the level of protection against UVA radiation.  

However, this kind of classification does not show precisely what kind of protection is in question, as in the case of SPF and UVB radiation. Lately a new kind of classification has begun to be used: PA+. Since UVA radiation prompts the activation of melanin that causes the skin to tan, certain groups have attempted to use the Persistent Pigment Darkening (PPD) Method to establish the ability of different products to protect against UVA radiation. The test is conducted by exposing multiple subjects to UVA radiation with one part of the skin protected and the other unprotected, after which the difference between the two observed.  The problem with this test and the reason why this kind of classification of UVA radiation protection has not become widely used is because there is no standardised system for evaluating the results. Due to the mentioned lack of standardisation in interpreting results, the same results are interpreted differently from country to country, depending on their various individual scoring systems. The biggest fault of the PA+ classification of UVA protection is that it focuses exclusively on skin tanning. The first problem of such an approach is that the variability is too great between the test subjects since some individuals tan much more easily than others, and the second is that UVA radiation has more problematic consequences that are invisible to the eye since they affect the deeper layers of the skin. The PA+ testing approach does not take these consequences into account.

Now let us briefly mention the different types of protection filters. You most probably know that filters are divided into two groups – chemical and physical. The main difference between these two groups is that chemical filters have a specific absorption spectre and protect in such a way that they absorb radiation having certain wave lengths. On the other hand, physical filters block the radiation from penetrating skin, in other words, they reflect it. In the past chemical filters were considered to be less capable of protecting against UVA radiation but today filters such as Tinosorb, Uvinul, Mexoryl and Parsol have been developed and they are very effective at fighting against both types of radiation. Chemical filters are in general more acceptable in cosmetic products, they are more easily incorporated into products and products that contain them spread easier, meaning that less product needs to be applied for equal protection. Their shortcoming is that they need to be applied on the skin 20 to 30 minutes before sunbathing in order for the protection to be adequate, but also the fact that they have a somewhat bigger potential to cause irritations on extremely sensitive skin. Physical filters are not as cosmetically sophisticated, both for the producers (they are difficult to spread, they have a thick consistency, they are harder to incorporate into formulations), and the users   (they may leave a white residue after application which is why people tend to apply too little). They offer protection immediately after application, and they are somewhat more stable and have a longer shelf life. In certain formulations they may wash off the skin while bathing and sweating but in general, reapplication is needed less often for physical than chemical filters. In other words, each of the two groups mentioned has its advantages and shortcomings. Your products will most often consist of their various combinations, with the aim of achieving optimum protection and at the same time, providing a satisfactory texture of the product.

In conclusion, there is one more fact that is very little known yet is of key importance for sun protection. Namely, everything we have already mentioned in this article (all research studies, determination of protection factor etc.) applies only if you apply your sunscreen correctly. Although you probably think that this is not so serious, that you must be applying your product properly and getting the promised protection, research has shown that only 30 to 40% of people apply SPF properly, while most of us get only 40% of the sun protection we think we are getting due to improper application. All research has been carried out using 2 mg of sun protection product per 1 cmof skin. Let’s translate that into more practical units. You should divide your body into 8 segments: head/neck, chest, upper back, arms, lower back, stomach, front part of legs and back part of legs. On each of those segments you should apply as much cream as you would need to make a thick line from the top of your middle finger to the bottom of the palm of your hand. If you are one of those people that use a single sunscreen product several years in a row, be aware that you are not applying enough and in fact, you are not as protected from the sun as you might think.

REFERENCES:

  1. Diffey BL, Grice J. The influence of sunscreen type on photoprotection. British Journal of Dermatology, 1997, 137, 103-105
  2. What Is Ultraviolet (UV) Radiation?, 2017, https://www.cancer.org/cancer/skin-cancer/prevention-and-early-detection/what-is-uv-radiation.html, accessed 4 July 2019
  3. Ask the expert: Does a higher SPF sunscreen always protect your skin better?, 2018, https://www.skincancer.org/skin-cancer-information/ask-the-experts/does-a-higher-spf-sunscreen-always-protect-your-skin-better, accessed 5 July 2019
  4. The sunscreen guide. For lost souls, 2018, https://chemistconfessions.com/basics/the-sunscreen-guide-for-lost-souls/, accessed 4 July 2019

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