Feeling lost in the face of the myriad of sunscreens and all these formulas that you don't really understand? We explain what SPF is, why it's important, and which treatment to choose.
What is an SPF?
In English, SPF translates as “Sun Protection Factor”, so if you see SPF (Sun Protection Factor) or IP (Protection Index) written on your bottle, they are the same thing.
The latter is defined as follows: It is the ratio between the minimum erythemal dose on skin protected by a sunscreen product and the minimum erythemal dose on the same unprotected skin. In other words, it is the time it will take your skin to get sunburned when it is protected.
To calculate it, laboratories expose volunteers to artificial UV rays by covering areas of their backs with different indexes in order to measure the time it will take for the skin to redden. For example, if it takes you 10 minutes to get sunburned without protection, with an index of 30 it will take you 5 hours to get sunburned (30x10=300/60=5h).
But several elements must be taken into account: The quantity of product applied to the skin (in the lab it is 2mg/cm2), the power of the UV rays, the phototype of each person as well as their sensitivity to the sun.
What does 15, 30, 50 mean?
The figure indicated on your sunscreen results from this famous calculation seen previously, but if we had to translate these into percentages, this would give the following measurements:
An SPF 15 filters 93%, and from an index 30 we obtain strong protection of 97% filtering up to 98% for an index 50.
Yes, you read that right, you only gain 1% protection between an SPF 30 and an SPF 50, the power of the filter will mainly depend on the duration of exposure and the quantity applied.
Which protection for which skin type?
The lighter your skin, the higher your SPF should be. So choose an SPF 50 that protects against UVA and UVB rays without leaving a trace.
The same applies if you're going to a vacation spot where the glare is very strong. In the tropics, in the mountains, or in the desert, apply SPF 50 regardless of your skin type.
At the beach or by the water, if you tan easily and rarely get sunburned, opt for an SPF 30 cream that protects and boosts your tan.
Finally, if your skin is black or mixed-race, a cream with an SPF of 15 is sufficient, provided you do not expose yourself for too long. This SPF is also ideal for continuing to protect your skin in the city after returning from vacation when the melanin is sufficiently activated.
In any case, avoid exposing yourself to the sun for too long, do not expose yourself between 12 p.m. and 4 p.m. and never expose babies and young children to the sun!
Anaïs Texier, E-commerce Manager at PAYOT
An expert skincare specialist, Anaïs deciphers skincare trends and shares her advice.