Contents / Sommaire
- 🇬🇧 Organic (chemical) vs inorganic (physical) sunscreens
- 🇫🇷 Les filtres solaires organiques (chimiques) et inorganiques (physiques)
Sunscreens are a must if you want to prevent photoaging.
After introducing Sunscreens 101 in Part 1, emphasized on what a broadspectrum sunscreen is and what kinds of filters are used, I’d like to focus on the differences between organic (or chemical) and inorganic (or physical) sunscreens. To wrap that part, I also discuss about micronisation, a technique used on inorganic filters, especially to avoid white cast (if you have no idea what this is, don’t worry, it’ll be explained) but under questions for safety reasons.
This article is part of the in-process Sunscreens and Your Skin series which deals with everything related to sunscreens (how they work, how to use them, how to choose them…).
In the other articles from the series, I have discussed:
- in Part 3, about the meaning of SPF, PPD, PA+… labeled on the packaging of a sunscreen.
- in Part 4, about some organic filters showing health risks.
If you are interested to know what sunscreens protect from, namely UV rays, you can access the thematic Ultraviolets and the Skin series.
🇬🇧 Organic (chemical) vs inorganic (physical) sunscreens
1. What are they?
In sunscreens, protection is provided by the filters incorporated in the product. Those are called active agents and their proportion in the formula determines the protection factors against UVA and UVB rays, responsible for photoaging and skin cancers.
Before diving into the pros and cons of each type of filters, let me remind you what these active agents are (you can also access Part 1 which introduces them):
Organic filters are organic molecules (usually containing a carbon atom). They absorb UV radiation within a specific range of wavelengths depending on their chemical structure and release the energy as lower-energy rays or by vibrating, thus preventing UV radiation from reaching the skin.
Avobenzone, octinoxate or Mexoryl XL are chemical type. They can be referred to as chemical absorbers.
- Inorganic filters reflect, scatter and absorb UV rays: they contain inert minerals such as titanium dioxide or zinc oxide. They can be referred to as physical blockers.
Each filter, chemical or physical, protects the skin from a specific range of the UV rays (UVA, UVB or both). To ensure the widest protection (broadspectrum), ranging from 290 nm to 400 nm of the UV spectrum, they are usually combined into full chemical, full physical or chemical-physical formulas.
Protection factors are measured with standardized protocols meaning that, when you compare sunscreens, an SPF 30 in one brand gives the same UVB protection as another sunscreens also labeled SPF 30 in another brand whatever the filters used are.
Nevertheless, If we set aside those labels giving information about the UVA and the UVB protection, one can pinpoint differences between organic and inorganic sunscreens.
2. Advantages and drawbacks of each type of filter
The table below indicates, for each type of filter, the pros (in green) and cons (in red) for several concerns. I have also put the meaning of certain terms below the table.
|Concern||Organic or chemical filters||Inorganic or physical filters|
|Cosmetic texture||More cosmetic friendly: the texture can be thinner and spreads more easily on the skin. Also, there is no white cast after application (see below for the meaning) making them more wearable for everybody.||Less cosmetic friendly: the texture is thicker and more difficult to spread on the face evenly. Also, they can leave a white cast (see below for the meaning) making them less wearable for people with darker skin tones.
However, if micronized (reduced in nanoparticles), the filters are more cosmetic friendly.
|Photostability||Less photostable under light: under sunlight, the protection can diminish, making them less protective through the day (1) without reapplication.||More photostable under light: the protection provided by the filters do not change under sunlight.|
|Irritations||Can be irritant: Studies showed that those filters can provoke allergies and irritations to the skin (3). The higher the SPF, the more irritative the sunscreen can be due to higher proportions of chemical filters.||inert: Studies showed less allergies and irritations as those filters are more inert to the skin, which can be interesting for sensitive skins (2), except when the product contains nanoparticles.|
|Other health concerns||Oxydation: some studies showed that those filters can release free radicals when absorbing UV radiation which can damage the cell’s DNA (1).
Endocrine disruptor: Octinoxate (Ethylhexyl methoxycinnamate) and oxybenzone have shown to have hormone-mimicking properties which can lead to developmental disorders (6).
|Micronisation: if the filters are micronized (between 15 and 50 nm), they are suspected to penetrate the skin layers (see Health concerns over micronisation below for more information).|
|Reapplication?||Yes, the sunscreen has to be reapplied at least every 2 hours when you are out in the sun, more if there are physical activities (5).||Yes, the sunscreen has to be reapplied at least every 2 hours when you are out in the sun, more if there are physical activities (5).|
White cast: a semi-opaque or chalky layer left by sunscreens on the skin which formula contains inorganic filters, like titanium dioxide or zinc oxide. This can be incompatible with medium to dark skin toned people or leave a grey undertone under makeup.
To conclude the comparison, industrials can get the most out of the filters by combining them.
3. Health concerns over micronisation
a. Safety information
To avoid the white layer induced by inorganic filters and increase the photoprotection, TiO2 (titanium dioxide) and ZnO (Zinc oxide) are micronized to particles below 200nm in size. At this dimension, the particles have different interactions with their environment and may be no longer inert: TiO2 has indeed been categorized as 2B carcinogen “possibly carcinogen to humans” by the International Agency for Research on Cancer (IARC), being responsible for lung cancers for people working in a dusty environment (4). On the other hand, the Food and Drug Administration (FDA) in the USA consider the TiO2 particles safe when used in UV filters.
b. Skin penetration
In vitro (in human cell culture) and in vivo (in real human skin samples) experiments done with nanoparticles of TiO2 and ZnO showed that on a healthy skin, nanoparticles could be detected but in the upper part only. However, on impaired skin barrier (psoriatic skin for example), a deeper penetration was shown for a few particles.
Experts emphasize the fact that more studies must be conducted to understand the penetration mechanisms and the impacts on the body. On top of that, there are existing approaches to counter those risk, like using coating agents that isolate the particles and thus minimize the interactions with the skin (7).
4. What to remember
In addition to the advice provided in Part 1, please keep in mind the following:
Each type of filter has pros and cons concerning the cosmetic texture, the photostability or health concerns:
- organic filters are more cosmetic friendly but are less photostable and can have irritative and some are suspected to be endocrine disruptors,
- inorganic filters are less cosmetic friendly if not micronized but are more photostable and inert. Hence, choosing a full inorganic sunscreen can be a good choice for people having sensitive skins,
- nanoparticles are more and more used but it is still not clear if they are harmful to our health when they penetrate the skin layers.
In the next articles, I will focus on the packaging labels so that you’ll be able to choose the right product and on some chemical ingredients (that I have talked briefly here) that you might need to watch out.
Do you prefer organic, inorganic or combined sunscreens? Leave a comment!