Photoprotectors are essential to protect the skin from the damaging effects of ultraviolet radiation. But what are SPFs and how is the protection of each sunscreen measured? 

How sunscreens work 

In photoprotective products, sunscreens are the ingredients that protect our skin from burns and erythema. These work by absorbing ultraviolet radiation from the sun, like filters of chemical origin, or by reflecting this radiation, like filters of physical origin. 

We talked previously about the different types of filters that are used in the formulation of sunscreens, you can find this information in a previous post. 

What is the Sun Protection Factor (SPF) 

The sun protection factor is a value that indicates how long we can be exposed to the sun’s rays. However, this time depends on the type of skin; For example, a person with phototype I has a type of skin that is highly prone to sunburn, so they should spend less time under the sun’s rays than a person with phototype V, who have more protection against this type of burn. 

 A high SPF, which we can currently find on the market, is SPF 50, which means that it will take us 50 times longer to burn than if we did not use photoprotection. 

In other words, if a person with phototype I spends about 10 minutes without protection (called DEM) and uses a photoprotector with an SPF of 50, it will take 500 minutes for her skin to start to redden. This value is obtained by applying the following formula: 

DEM (10 minutes) x SPF 50 = 500 minutes 

However, this is not an exact rule and depends on multiple factors, in addition to the skin type. Therefore, dermatologists recommend applying photoprotection every 2 hours, to obtain adequate protection. 

SPF levels 

There is a protection classification based on the sun protection factor of each product 

As we indicated in the previous post, the higher the SPF, the greater the protection. However, the difference in UV radiation that sunscreens can filter out is never 100%. Thus, sunscreens with SPF 15 filter out about 93% of UVB rays, while sunscreens with SPF 30 filter out about 97% and those with SPF 50 filter out about 98%. In other words, no sunscreen provides total protection but, according to the FDA (American Food and Drug Administration), sunscreens with a factor lower than SPF 15 only protect against sunburn, but not in the development of skin cancer due to solar exposure 

How is SPF measured? 

 The measurement of the protection factor of a solar product should be done following the COLIPA guidelines. This body is the European Trade Association. 

Image by Tara Winstead from Pexels

According to these guidelines, the sun product should be applied to healthy volunteers with phototypes I, II and III. In such a way that the resulting SPF will be the average of the results in the three skin types. 2mg of product is applied to different areas of the back and is subsequently irradiated with UV light until the skin turns red. Once the time that the skin has taken to turn red (DEM) has been calculated, the SPF is calculated according to the formula that we saw previously. 

How to choose a suitable sunscreen? 

To choose a good sunscreen, we must first take into account our phototype: the lower the phototype, a protector with a higher SPF will be recommended. On the other hand, photoprotectors include more ingredients in addition to sunscreens: antioxidants, vitamins, and moisturizing compounds that keep the skin hydrated while protecting itself from the sun. Therefore, in addition to the desired protection factor, we can find various options on the market that best suit our skin type. 


    Cover image by Mikhail Nilov from Pexels