A classic summer product, sunscreen is more complex than it seems. The filters that protect us from UV rays use the most advanced technologies. But what exactly are they used for? What protection factor should you choose, and above all, what precautions should you take to ensure optimal effectiveness?

What are sunscreens used for?

In summer, the skin is attacked by repeated exposure to the sun. "The sun's ultraviolet rays (UVA and UVB) attack the skin like a shell would attack a barrier in an enemy camp," explains Dr. Catherine Gaucher, a dermatologist and venereologist in Paris. "Our cells have barriers of essential fatty acids, and when UV rays arrive, they penetrate this barrier by making singular oxygens that can be harmful to the cell and the cell nucleus, and attack the DNA," she continues.

Thus, the sun is responsible for sunburn, premature aging of the skin as well as the appearance of skin cancers. "At some point, when DNAs have been attacked frequently, the cells end up with abnormal DNA, which can then give birth to a cancer cell," notes Dr. Gaucher. "Apart from cancer, cells that are repeatedly damaged age faster. A solution: protect yourself from the sun by applying a sun protection!

Sunscreen: definition, how does it work?

The solar filter is the essential component of the products of solar protection. It is what makes "barrier" in front of UV.  

There are two types of ultraviolet filters:

  •     Mineral or inorganic filters, which remain on the surface of the skin: "they act mechanically, like a mirror that reflects the UV at the time it arrives on the skin", comments Dr. Gaucher. This filter contains minerals in nanometric form (molecular scale): molecules of talc, titanium dioxide, zinc oxide, etc.. These nanoparticles present in the sun cream are responsible for these white traces left on the skin when the product is applied. They are often found in sun creams for children or sensitive skin, because they minimize the risk of allergy;
  •     Chemical or organic filters, which are "a substance that absorbs a lot of the UV rays from the skin cells," notes Dr. Gaucher. When it is in the skin, it immediately traps the UV rays, which are less numerous thereafter to attack the cellular membranes". Passing the skin barrier, they were suspected to be a source of allergy. Today, the molecules of these filters are "bigger" and remain on the surface. The risk of reaction is less.

If the common goal of these two filters contained in the solar products is to protect the skin from the sun, they do not work in the same way

Sunscreen: the difference between chemical and mineral filters

They do not work in the same way: the mineral filter reflects UV rays like a mirror, the chemical filter absorbs them. However, the result is similar, as is their effectiveness: they both protect the skin from the harmful effects of UV rays. "The real difference between a mineral filter and a chemical filter is what we call the galenic (pharmaceutical form of the drug)," explains Dr. Gaucher. Indeed, sunscreens with mineral filters are white, their texture is less fluid, and this hinders their use.

The consequence is that you put it on for less time, less often, or not enough in terms of quantity," she observes. "As creams with mineral filters more difficult to wear, it is more difficult to respect the instruction which would be to put a full sunscreen in the morning, every day from May until September". A badly applied cream is an ineffective protection, and therefore a real danger!

It should be noted that today, more and more organic filters have become invisible because they have been reduced to nanoparticles: their pigments, much smaller, are no longer or almost no longer visible.

Solar filters: are they dangerous?

One of the dangers is therefore the bad evaluation of the protection. "Without forgetting that a filter plunged into the water during swimming, at a rate of two times in the space of 20 minutes, is no longer effective," notes Dr. Gaucher. "Or if a filter has been spread out too much, it's no longer effective either. That's why I recommend, in addition to applying sunscreen, wearing UV protective clothing, hats, etc."

"For overall health, mineral filters are more reassuring," notes Dr. Gaucher. "Their advantage is that there is no risk of chemical interaction in the body; but the disadvantage is that they are not effective if you don't put them on correctly, because you don't want to be all white all the time!" she reminds us.

Studies have shown that you need to adhere to the right thickness of cream for the given surface. "For the dose of a filter to be active, the amount of cream put on the last phalanx of your index finger must correspond to a skin surface equivalent to twice the palm of the hand," explains the dermatologist.

Sunscreens and endocrine disruptors

The debate began in 2004: Margaret Schlumpf, from the Institute of Pharmacology and Toxicology at the University of Zurich, tested nine molecules used in cosmetics and sunscreens on rats and mice, using high-dose injections. The result: six of the tested substances disrupt the proper functioning of estrogen in rats. Most cosmetics manufacturers have pointed the finger at the methodology of the study, stating that it is obvious that injected at massive doses, the effects are not the same.

Now, other studies have proven that sunscreens are endocrine disruptors. A recent study conducted by researchers from the Laboratoire de biodiversité et biotechnologies microbiennes de l'Observatoire océanologique de Banyuls-sur-Mer (Sorbonne University/CNRS) reported that octocrylene, an organic filter present in sunscreens, degrades within the bottles themselves into a known carcinogenic and endocrine-disrupting compound: benzophenone-3 (Source 1).

The particular case of titanium dioxide

Titanium dioxide (TiO2) is used in many cosmetic products. "In sunscreens and beauty products, TiO₂ (Cl 77891) nanoparticles have been evaluated by the Scientific Committee on Consumer Safety (SCCS) (see April 2014 report entitled 'Opinion on Titanium Dioxide (nano form) COLIPA No. S75 (SCCS /1516/13)' (Source 2) which approved their use as anti-UV, with an authorization of a maximum concentration of 25% (applications in the form of spray are not allowed)", indicates the site cancer environment (Source 3).

However, it is the inhalation of titanium dioxide that would pose a problem for health. On February 18, 2020, the Official Journal published that among six ingredients used in cosmetic products, "titanium dioxide (Titanium dioxide) officially becomes a category 2 carcinogen by inhalation," reports the site.

Sunscreen and destruction of corals in the oceans

Another subject of controversy: the destruction of the aquatic environment and marine life by the components of sunscreens. Indeed, the latter are accused of killing the micro-algae contained in the coral tissue. A subject that divides the scientific community: in 2014, a study conducted on the Balearic Islands reported that particles of titanium dioxide and zinc oxide destroy plankton (Source 4) but since then, other studies have proven the opposite: they are actually only slightly toxic. Other studies report that more important factors are responsible for coral bleaching, such as global warming.

Note: organic sunscreens contain the same mineral filters as conventional sunscreens. 

Sunscreen: what to choose as cream and filter?

In order to avoid sunburn and other dangers, such as premature aging of the skin and skin cancer, it is useful to choose your sunscreen and apply it correctly. To begin with, according to the regulations in force, a sunscreen product must protect against both UVA and UVB rays. Then, choose the right protection factor according to your skin tone and your exposure situation, and finally the format in which it is presented: cream, mist, spray, etc. Don't forget to protect your eyes from UV rays by choosing a good pair of sunglasses!

Then, you can choose sun creams with either mineral or chemical filters. In any case, it is important to know that cosmetic laboratories often mix several filters in the same cream in order to provide the right protection.

Natural sunscreen: can you make your own sunscreen?

No! It is impossible to make your own natural sunscreen because it will not contain the ultraviolet filters that protect against UVA and UVB rays. It will therefore be ineffective. However, you can find organic sunscreens on the market that use only mineral filters, or you can choose a sunscreen with a mineral filter.

Sunscreens: A classification of indices finally simpler

For a long time, we got lost in the indices: 15, 20, 30... From now on, a "category" is attributed to them to designate the strength of the protection. In addition, the anti-UVA protection is now codified. "It must represent at least one third of the UVB protection. If you buy a cream index 30 (anti-UVB), you have an anti-UVA protection of at least 10", explains Dr. Jean-Romain Manciet, dermatologist. In addition, if cosmetic laboratories wish to market a sunscreen product today, they are obliged to choose from a positive list of sunscreens authorized by the health authorities (27 in total).

To know :

  •     Low protection: from 6 to 1.
  •     Medium protection: from 15 to 25.

  •     High protection: from 30 to 50.
  •     Very high protection: 50 +.
Day creams with a sun filter?

More and more cosmetic brands are offering day creams with SPF (meaning Sun Protection Factor), i.e. day creams that contain protection from the sun's ultraviolet rays. If the day cream with a solar filter can be a good daily solution, it does not replace a classic solar cream, which will be more effective, and will protect you much better from UV rays during exposure to the sun.

Some simple rules to protect yourself

- Apply sunscreen on all exposed areas and up to the tips of your ears.

- Reapply every two hours.

- Stay in the shade during the hottest hours (11 a.m. to 4 p.m.).

- If the filters are organic, wait 20 minutes between the time you apply the cream and the time you expose yourself, while the filters activate. 


Source 1 : Article ''A filter present in many sunscreens turns into a carcinogenic compound'', CNRS website (national center for scientific research), March 8, 2021.

Source 2 : April 2014 report entitled ''Opinion on Titanium Dioxide (nano form) COLIPA n° S75 (SCCS /1516/13)''.

Source 3 : Article "Titanium dioxide (TiO2), food additive (E171)", Cancer Environment website.

Source 4: Study 'Sunscreens as a source of hydrogen peroxide production in coastal waters', David Sánchez-Quiles, Antonio Tovar-Sánchez, 2014.