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What is the sun protection factor?

We are all familiar with the term “sun protection factor” (SPF), but do we know what it refers to?

To explain it simply, the SPF indicates how much longer our skin can last without turning red after the application of sunscreen (compared to the same skin without sunscreen). For example, if an individual can stand 10 minutes in the sun without getting sunburned, after applying a filter of 30, he/she would stand 300 minutes without getting sunburned.

The sunscreen is measuring only one of the short-term effects of UVB radiation (redness) (but not other long-term effects, nor the consequences of other radiation that also affect the skin).

Interesting to know that this SPF measurement is based on the application of 2 mg/cm.² of photoprotector on the skin, it is known that this amount is higher than what is usually applied by patients… In addition, in many cases it is not applied homogeneously, it ends up being removed by sweat, water and sand, and we do not reapply it. Therefore, the FPS is often overestimated.

Another interesting point is that this protection indicated by the SPF is not linear, meaning that when we talk about SPFs higher than 30 (30, 40, 50) the difference in its protection capacity is minimal. An SPF above 30 is considered high, and above 50 very high.

SPF measures the ideal burn protection situation: it assumes sufficient product application. It is a measurement made on volunteers, in a laboratory. Variations in altitude, cloud cover, latitude, time of day… can modify this value in real life.

What is a sunscreen and what types are there?

A photoprotector is a cosmetic product prepared for application to the epidermis to protect us from radiation. The most important element of a sunscreen is its sunscreen (or filters), but it contains other components that can affect the efficacy of the product. The correct choice and combination of all these ingredients influences their quality. The SPF on the package indicates only one of many product characteristics:

– Organic or chemical filters absorb radiation and release it as heat to the skin. They are more cosmetic than physical filters, but may also be absorbed systemically. They may cause irritation or allergies.

– Inorganic or physical filters act as a screen that reflects or scatters radiation. They rarely cause sensitization, so they would be more appropriate for people with sensitive skin.

– These two types of filters are usually combined to achieve wider coverage. As I mentioned before, SPF only measures protection against a UVBR effect.

I bought a very cheap sunscreen at the supermarket, also with SPF 50, aren’t they all the same? Why pay more for the same?

They are not at all the same:

– Not all of them protect against the same spectrum of radiation: not only UVB, but also UVA, visible light and infrared.

– the combination of different sunscreens improves the product, but not all are equally effective, safe or compatible with each other.

– The stability of the formula is essential: it is useless for a sunscreen to have an SPF of 50 if it degrades in half an hour.

– The addition of other substances such as DNA repair enzymes or antioxidants can slow or reverse cell damage. DNA repair enzymes are proteins that can repair DNA defects caused by UVR. They are not present in humans, but can be incorporated into photoprotectors; in vivo and in vitro studies support the benefit of these enzymes in photodamage prevention. As for antioxidants, their addition to sunscreens adds benefits over sunscreen alone. Some of these topical antioxidants are soybean extract, vitamin C, vitamin E, grape seed extract, tea polyphenols, selenium, melatonin, silymarin or aloe vera extract.

– Be “water resistant”, or “very water resistant”, or sweat resistant. But it is important to note that there is no such thing as a “waterproof” or “sweatproof” photoprotector, neither 100% nor “all the time”.