Prof. Luca Valgimigli
Sunscreens or UV filters are natural or synthetic compounds that are included in cosmetic formulations to protect the skin from damages caused by solar exposure.
In the case of specific sunscreen formulas (to be used for sunbathing), they are responsible for the Solar Protection Factor, SPF, whose value indicates the degree of protection the formula will guarantee to our skin, thereby avoiding erythema and other damages like photo-aging.
What do UV filters exactly do and how do they act?
The principle is very simple: UV filters reduce the amount of solar radiation reaching the surface on which they are applied, for instance skin surface. The difference among the many UV filters lies in the mechanism by which they achieve this goal.
Physical filters reflect (back) a portion of solar radiation, letting only a limited fraction of light cross them and reach the skin. Therefore, they do not interact with solar radiation and they are not altered by it at all.
Chemical filters, instead, absorb a portion of solar radiation, and use it to achieve a higher quantum energy state. Immediately after, such excess energy is released to the environment in the form of heat, thereby making the filter ready to absorb solar energy again.
The different mechanisms of action are summarized in the picture on the left. In both cases, the amount of solar energy allowed to pass (which is not reflected or absorbed) depends on the amount of filters applied on the skin, which determines the solar protection factor.
Both types of filters offer advantages and disadvantages: physical filters have the advantage of being completely stable and not being damaged by solar radiation. Furthermore, compounds like Zinc oxide are totally inert and are very safe for skin. Their disadvantage lies in the difficulty to reach high SPF values without causing the so-called “white effect”. In order to reduce this effect, it is possible to use them in micronized form, which is much more precious (BeC uses this form in all sunscreen formulas). However, even micronized forms do not allow reaching high protection without becoming “visible” on the skin.
Therefore, in high protection formulas they are usually combined with chemical filters. Chemicals filters, infact, have the advantage of being very effective and of offering excellent performance while being completely invisible. They disperse very well in the formulation affording a more homogenous protection (corresponding to a more even tan!); however, since they absorb the solar energy, they are subjected to the risk of photo-degradation, or they could undergo photochemical reactions.
At this point, let’s better clarify a very important aspect. Often, the expression “chemical filter” is confused with “synthetic filter”, i.e. artificial, while it is generally believed that physical filters are natural. This is not necessarily true! Physical filters are normally inorganic, i.e. minerals, and normally they are natural, but they can as well be synthetic, i.e. artificially produced.
On the other hand, the most common chemical filters are often synthetic, i.e. man made; however, there exist also examples of natural chemical filters. Among the most important ones, there is certainly gamma-oryzanol, which is extracted from rice bran (see picture on the left), and other examples are cinnamic acid, typical of cinnamon but found also in Brassica vegetables (cabbage, broccoli, etc) and in shea butter, carotenoids(e.g. from carrots, tomatoes and several red-orange fruits), Vitamin E and many more.
These compounds have also the advantage of possessing additional properties (e.g. antioxidant, soothing, calming, anti-age); unfortunately, however, they are not as effective as synthetic chemical filters. BeC uses natural chemical filters when high SPF values are not requested (e.g. in Huile SolE’), but when these are needed, synthetic chemical filters must have been combinate.In conclusion, don’t be fooled by the words: chemical or physical filters indicate their mechanism of action not their origin. The origin can either be natural or synthetic, but the most important aspect is their stability toward solar radiation, which is fundamental for our safety under sunlight.