SPF stands for “sun protection factor.” In general, the SPF number indicates how long the skin can be exposed without burning to UV radiation.
How is it calculated?
The SPF depends on skin phototype. In the case of skin that, with given radiation, takes 10 minutes to redden (DEM: minimal erythematogenous dose), if an SPF of 30 were applied, it could remain in the sun for 300 minutes without burning, the SPF 30 will provide 5 hours of protection.
As you imagine, the calculation of the SPF depends on multiple factors, on the characteristics of the skin, on how it is protected (tanned) at that time of year, from solar radiation, which in turn depends on latitude, on the weather conditions and the hours of incidence or exposure.
So, with a high FPS (50, for example), would it be enough to last a whole day at the beach?
The answer is resounding: “no.” If we use the previous DEM (10 minutes), with an FPS of 50, we would have for 500 minutes of exposure, more than 8 hours. However, the calculation is not that simple.
We must bear in mind that not all sunscreens are the same or protect our skin in the same way. We know that products that contain SPF, basically sunscreen, must be perfectly absorbed to provide those protection values. The calculations are very arbitrary and depend on many factors, such as the skin’s absorption capacity, thickness, intrinsic characteristics, and the temperature and environmental conditions or contact with water.
Factors influencing FPS
One of the factors that should most influence SPF’s choice is the skin phototype, since the lower the natural pigment of the skin, the higher the SPF of the product we use should be.
Remember what skin type you have to know which product will be most useful for you and your skin’s health:
- Phototype I: always burns and never pigments.
- Phototype II: always burns and is slightly pigmented.
- Phototype III: rarely burns out and gradually pigments.
- Phototype IV: never burns and always pigments.
- Phototype V: pigmented races.
- Phototype VI: black race.
We are not going to fool you; the FPS calculation is confusing. Depending on the product, it may have been obtained using different values and vary from one pharmaceutical laboratory to another depending on the amount of product applied per unit area and the type of light source used, which means that these products are not always comparable.
Another concept often linked to sun protection products is the translation of SPF into English SPF ( sun protection factor ), which measures protection against UVB rays. There is also the PPD ( persistent pigment darkening ), which is the index that measures the ability to produce long-lasting or immediate pigmentation of the skin, and that indicates protection against UVA rays.