If you follow the cosmetic scene, you probably know that us bloggers fight a lot and constantly emphasize how important daily sun protection is. Of course, it is no surprise that our campaign intensifies before summer, as we want to reach as many people as possible with our messages. And if we cannot convince people not to expose themselves to the sun, we want to at least convince them to protect themselves with sunscreen while being exposed. It is only in the last few years that we have actually begun to realize what effects UVA rays can have on the skin.
Quick repetition about UV light
UV stands for ultraviolet waves, which are part of the electromagnetic spectrum. All light rays, including UVA and UVB rays, have different wavelengths measured in nanometers or short “nm”.
The UV spectrum comprises wavelengths between 100 and 400nm. There will be no further information about UVC rays because they are trapped by ozone. However, we need to pay so much more attention to both UVB and UVA protection.
UVB light has a much smaller wavelength range (290-320nm) than UVA light. UVB light is directly responsible for the formation of sunburn and other visible changes on the surface of the skin. UVB radiation plays a role in the development of skin cancer. Unlike UVA rays, the intensity of UVB rays varies considerably depending on the geographical location, time of day and time of year. Like UVA light, UVB light is present throughout the year, but UVB rays are weaker in case of cloudy weather.
UVA light represents about 95% of the UV light that falls on Earth. The UVA spectrum has a significantly wider wavelength range and is divided into two parts UVA2 (320-340nm) and UVA1 (340-400nm). UVA rays are present throughout the day, throughout the year, even when it is cloudy and pass through the glass. They are considered silent killers because, unlike UVB rays, you do not see the harmful effects of UVA rays immediately. UVA rays cause the skin to tan. Even if the sun didn’t burn you and you didn’t develop redness, but you tanned anyway, it means that UVA rays have reached deep into the skin and caused damage to the skin and melanocytes there. UVA rays penetrate deeper into the skin than UVB rays, constantly destroying key substances in the skin that ensure the firmness and elasticity of the skin.
How do we actually measure UVB protection?
The level of protection against UVB rays is marked with SPF or sun protection factor. SPF tells us how much UVB rays sunscreen protects us from. We know sunscreens with low protection (SPF 5-15), sunscreens with medium-high protection (SPF 15-25), sunscreens with high protection (SPF 30), and sunscreens with extremely high protection (SPF50 and SPF50 +).
But how do we actually measure UVB protection? The most common method of measuring UVB protection is performed on human skin, where it is determined how quickly the skin turns red in UVB light if it is not smeared with sunscreen, compared to if it is. Because the method is performed on human skin (a living organism), it is called the in vivo method. How SPF is measured in vivo is determined by ISO standards. You can think of ISO standards as one set of rules that prescribes just about every parameter, from how many wavelengths we take for irradiation, to what test subjects we choose, and how we measure certain parameters on them. We know 2 ISO standards, one is used in Europe and elsewhere in the world, and the other is used in the USA.
How much UVB rays our sunscreen actually protects us from can be easily calculated with the following equation:
Conversions between % of blocked UVB rays and SPF
UVB (%) = 100 % – 100 % / SPF
SPF = 100 % / (100 % – UVB (%))
Let’s give an example of computing on SPF30 and SPF 50.
UVB (%) = 100 % – 100%/30 = 96,6 %
UVB (%) = 100 % – 100%/50 = 98 %
It may seem at first glance that this is only 1.5% of the difference. But we have to look at how much radiation our sunscreen emits (1 / SPF * 100%). SPF 30 transmits as much as 3.3% of UVB radiation, while SPF 50 transmits only 2%. But about why it is better to choose SPF50 than SPF30 a little later.
Since when are we aware of the importance of UVA protection?
Until a few years ago, we did not realize how important protection against UVA rays is, so manufacturers happily sent sunscreens to the market with UVB protection, but without UVA protection. When articles about the effect of UVA rays on the skin began to appear in reputable scientific journals, we began to realize that it would be necessary to look at UVA protection in sunscreens as well. Mini revolution, but not at all, because countries couldn’t agree on a single measuring system and labeling, so today you can find several different types of labels for UVA protection on sunscreens, which leads to consumer confusion and a lot of ambiguity. The problem is that instead of agreeing on a single measurement system, countries prefered to set up their own. That is why today we know the European, Japanese, British, American and Australian standards.
Why didn’t they introduce a uniform measurement system?
The biggest problem is that when the skin is irradiated with UVA rays, it does not react in the same way as when irradiated with UVB rays. The problem is that it depends on the characteristics of the skin of each individual, how he will react to irradiation with UVA light, while the response to irradiation with UVB in all will be the same – the development of redness. Some who are more prone to hyperpigmentation and have more sensitive skin will develop tanning faster and more intensely than someone who is not prone to hyperpigmentation.
Another problem, however, is that the spectra of UVB and UVA light are very close together and we cannot practically separate them. Some wavelengths of UVB light cause darkening of the skin, just as some wavelengths of UVA light can cause redness. All the confusion in short.
How does the skin react to irradiation with UVA light?
After contact with UVA light, immediate pigment darkening or IPD first occurs, which is a reaction where the skin first darkens slightly quickly because oxidation of the pigment melanin occurs. However, this initial darkening is short-lived because it fades within 2 hours. Initial darkening is caused by UVA and visible light (VIS). However, if we irradiate the skin with the full spectrum of UV light, tanning which remains occurs. This is called persistent pigment darkening or PPD. This tanning remains because the amount of melanin in the skin increases. Such tanning causes all the above-mentioned adverse effects, from the breakdown of collagen, the formation of hyperpigmentation,…
The second part of the post is coming, in which I will present the ways of marking and testing UVA protection!