One in 5 French people do not use sunscreen, and only 20% of users remember to reapply it every 2 hours. This negligence makes sense when we understand the difference between chemical filters and mineral filters. In fact, these two types of photoprotection do not work the same way on your skin at all. Chemical filters require 20 to 30 minutes to become active, while mineral filters work immediately. Beyond this time of action, their composition, skin tolerance and effectiveness vary considerably. In this article, we explain how to choose the sun filter suited to your skin type for optimal protection against UV rays.
Chemical filters and mineral filters: what really differentiates them?
How do chemical (organic) filters work
European regulations currently authorize 30 UV filters, the majority of which belong to the category of chemical filters. These organic filters operate using an ultraviolet light absorption mechanism. Their molecular structure is based on aromatic compounds with chromophoric groups, usually conjugated double bonds or carbonyl groups.
When these molecules receive ultraviolet radiation, they go into an excited state and then return to the stable state by dissipating the energy received in the form of heat. Chemical filters penetrate the upper layers of the skin where they convert UV radiation into a less aggressive form. This absorption occurs before UV rays reach skin cells, providing photoprotection against UVA and UVB rays.
How mineral (physical) filters work
On the other hand, only two mineral filters are authorized by European regulations: zinc oxide and titanium dioxide. These mineral filters are inert and opaque powders which act mainly by reflection and diffusion of UV radiation. Contrary to popular belief, mineral filters do not only act like mirrors. They also absorb part of UV radiation.
Mineral filters do not penetrate the skin but remain on the surface. Their photoprotective action is based on their ability to reflect and diffuse UV rays, but also to absorb part of them in the upper layers of the skin. This dual mechanical and physical action explains their effectiveness against UVA and UVB.
The difference in how they work on your skin
The fundamental distinction between these two types of filters lies in their interaction with the skin barrier. Chemical filters require penetration into the epidermis to become active. This absorption requires 20 to 30 minutes after application, during which your skin remains vulnerable to UV rays.
Mineral filters immediately form a protective barrier on the surface of the skin. Their reflective and diffusing action becomes effective upon application. This difference in mode of action directly influences the skin tolerance and comfort of use of each type of sun filter.
The impacts of each type of filter on your skin
Skin tolerance: chemical filters vs mineral filters
Skin tolerance varies considerably between generations of sun filters. Older generation chemical filters cause irritation or redness on sensitive and reactive skin. On the other hand, new generation organic filters are well tolerated by the skin and considered non-toxic.
Mineral filters have excellent skin tolerance, including for sensitive and atopic skin. However, their nanoparticle version raises concerns. Nanoparticles can enter the bloodstream and cause oxidative stress. Less than 0.03% of zinc nanoparticles penetrate the upper stratum corneum. It is still not recommended to apply nano mineral filters to irritated, very dry skin or skin with eczema.
Photoprotective effectiveness and duration of protection
Old chemical filters degrade quickly under the influence of sunlight. On the other hand, new generation organic filters offer reliable and consistent long-term protection.
Mineral filters retain their protective power over a long period of time thanks to their excellent heat resistance. However, they are less resistant to water and friction, requiring regular reapplications.
Texture and comfort of daily application
Chemical filters allow you to obtain fluid, transparent and easy-to-spread textures. Mineral filters leave unsightly white marks on the skin when they are not reduced to nanoparticles.
Which sunscreen for sensitive skin?
For sensitive, reactive or atopic skin, mineral filters remain the recommended choice. Their physical action limits the risk of irritation. Also, new generation chemical filters are suitable for sensitive skin provided you choose suitable formulations. Avoid products containing octocrylene or oxybenzone if you have a history of allergies.
Advantages and disadvantages of each solar filter
The strong points of new generation chemical filters
New generation organic filters offer remarkable photostability which allows them to maintain their effectiveness without degrading in sunlight. Their low comedogenicity makes them suitable for sensitive skin or skin prone to imperfections. These technologically advanced molecules protect against long UVA rays which penetrate deeply and cause skin aging.
Their light texture penetrates quickly without leaving a sticky or greasy film. For dark skin, these filters are particularly interesting because they leave no white residue. Their resistance to water and perspiration makes them efficient during outdoor activities.
The limits of old generation chemical filters
Traditional filters like octinoxate, avobenzone and homosalate cause allergies or irritation. Their instability to light poses a problem since the majority of older generation chemical filters are considered photo-unstable. Certain filters such as oxybenzone and octocrylene act as endocrine disruptors.
The environmental impact remains worrying. Around 10% of the world's coral reefs are threatened by solar filters responsible for their bleaching. Oxybenzone proves fatal to corals by destroying the symbiosis between the coral and its internal microalgae.
Why do mineral filters leave white marks?
Whiteout mainly comes from mineral sunscreens based on zinc oxide and titanium dioxide. These naturally white minerals stay on the surface of the skin and reflect light. The higher the sun protection factor, the greater the quantity of mineral screens will be. Larger mineral particles reflect more light and make the white layer more visible.
The debate over nanoparticles in sunscreen
Only five solar filters are authorized in the form of nanomaterials by European regulations. Inspections carried out in 2022 revealed that 13 products contained sun filters in the form of nanomaterials that did not comply with the particle size limits set. Titanium dioxide nanoparticles are safe if applied to healthy skin without exceeding a concentration of 25%. However, breathing nanoparticles can result in lung toxicity and inflammation.
How to choose the right sunscreen for your skin type
Choice criteria according to your phototype
Your phototype determines the level of protection needed. Phototypes I and II require SPF 50+ minimum. Phototypes III and IV can opt for an SPF 30 to 50 depending on the intensity of exposure. Phototypes V and VI are satisfied with an SPF 15 to 30. However, even with dark skin, protection remains essential against skin aging and skin cancer.
Understanding SPF and UVA/UVB protection
SPF measures protection against UVB rays responsible for sunburn. SPF 30 blocks 96.7% of UVB, while SPF 50 stops 98.3%. Regulations require that UVA protection corresponds to at least one third of UVB protection. Thus, an SPF 30 cream must guarantee UVA protection of at least index 10.
Oily, dry or sensitive skin: which filter to choose
Oily skin requires non-comedogenic formulas with fluid or gel textures. Dry skin prefers nourishing milks or creams with SPF 50 minimum. For sensitive skin, mineral filters without perfume or alcohol are still recommended.
For a sunscreen buying guide, read this article. https://www.quechoisir.org/guide-d-achat-creme-solaire-n4471/
Mistakes to avoid when applying
Apply 2 mg per cm² of skin, or approximately 35 g for the entire body. Application should be done 15 to 30 minutes before exposure. Renew every two hours and after each swim.
Chemical and mineral filters each have distinct benefits depending on your skin type. Without a doubt, the key lies in choosing a formula that suits your needs rather than the type of filter itself. We recommend that you choose new generation filters for optimal protection. Don't forget the essential: systematically apply your sun protection and renew it every two hours to maintain the health of your skin over the long term.
