How to choose the protection factor of sunscreens, the complete guide.
What is sunscreen protection factor (SPF)?
The protection factor of sunscreens (better known as SPF, or Sun Protection Factor) indicates the ability of the sunscreen to shield UV rays . It is generally expressed as a number and essentially refers to the percentage of UV rays blocked , which depends on the concentration of the sunscreen contained in the product.
When talking about SPF it should be specified that there is an in vivo SPF, measured on humans, and an in vitro SPF, measured with special equipment called spectrophotometers. The in vivo SPF is the ratio between the quantity of UV (and mainly UVB) necessary to produce minimal erythema on protected skin , compared to unprotected skin, when a volunteer is subjected to standardized irradiation. Mathematically we can define the SPF (especially in vitro) as the inverse of the quantity of UVB rays that reach the skin, so UVB = 1 / SPF. This means that, for example, an SPF of 50 indicates that the UVB that reaches the skin corresponds to 1/50 of the total quantity of UVB irradiated, equal to 2% (and therefore 98% of the UVB rays are blocked) .
According to the recommendations of the European Commission, the SPF factor must also guarantee a blockage of UVA rays equal to at least 1/3 of UVB rays .
SPF can be expressed in different ways, as reported in Br J Dermatol. 2009;161(Suppl. 3):13-24. This means that there is no single, standard definition of SPF. The European Commission requires that SPF values lower than 6 not be reported on the label .
When expressing an SPF value, that number should indicate a range: for example, if we write SPF=20 it means that the real SPF value is between 20 and 24.9 .
For this reason it is preferable to express the SPF as a protection class :
- low (SPF between 6 and 10)
- medium (SPF between 15 and 25)
- high (SPF between 30 and 50)
- very high (SPF greater than 50)
Sonia Olivieri face and body sunscreens comply with all European Commission directives and are available in three different formulations, which are distinguished by protection class: low, medium and high.
DISCOVER THE ENTIRE RANGE OF SONIA OLIVIERI SUN PRODUCTS NOW.
Is there a full screen?
Total protection means that you have 100% UV blockage . This can only be achieved with mechanical protection (such as clothing); sunscreens cannot guarantee total protection simply because it is impossible to completely cover a body surface.
Sonia Olivieri high protection sunscreens can screen out 99% of UVB rays .
