• Favoring natural ingredients is a strong current trend in perfumes and cosmetics, according to our partner The Conversation.
  • However, synthetic ingredients are not necessarily "worse" than their natural counterparts.
  • This analysis was conducted by Géraldine Savary, teacher-researcher in sensory analysis in the field of flavors, perfumes and cosmetics, and Catherine Malhiac, teacher-researcher in organic and macromolecular chemistry (both at Le Havre Normandy University).

Everyone uses cosmetics on a daily basis. Creams, gels, shampoos, sun and hair products... They are indeed essential to clean, protect and maintain our skin, teeth or hair. Beyond this aesthetic use, they also contribute to our health, limiting premature aging of tissues or protecting us against UV A and UV B from the sun so dangerous for our skin in terms of sunscreens.

Nevertheless, a real awareness has been made in recent years about these ubiquitous products.

Studies have, for example, suspected some of containing endocrine disruptors. These concerns are pushing more and more consumers to favor those who put forward reassuring arguments: absence of allergens, perfume, 100% natural, etc.

In fact, cosmetics often contain many ingredients – which can be questionable. Thus, a simple moisturizer can count several dozen: moisturizing agents, fatty substances, surfactants, preservatives, active ingredients ... and perfumes.

What impact for perfumes?

Perfumes are usually made from various compounds: natural or synthetic molecules combined with plant extracts, such as essential oils, assembled to create a pleasant scent.

Favoring natural ingredients is a strong current trend in this field. Among the most used are essential oils of lavender or sweet orange that are composed of molecules such as linalool or limonene.

Why this precision? Because these two natural molecules are not, contrary to popular belief, safe. Their use is also regulated in cosmetic products because they are allergenic – linalool can cause eczematous reactions. Their presence must be indicated on the labels of cosmetic products.

It is not because a molecule is of natural origin that it is harmless! If it is used, it is because it has an effect... It's all about quantity.

Wouldn't it be simpler to favor an unscented – and allergen-free – cosmetic product?

Fragrance-free cosmetics?

We must briefly return to the roles of perfumes added to our skincare products. There are three main ones:

  • Create a pleasant smell and feel. When we apply a cream on our face, and therefore near our nose, it is more pleasant to associate a pleasant smell ... There are also smells that are attached to a specific brand and that convey a positive valence. This is the case of the emblematic perfume of the famous blue pot creams;
  • Amplify the effectiveness of the product. Some perfumes can have a soothing or vitalizing character that can intensify its action. It can be cognitive or physiological – for example with a calming effect on the heart rhythm;
  • Hide the smell of other ingredients. Some plant extracts used as anti-aging active ingredients have unpleasant odors and can hardly be used alone.

When you develop a fragrance-free product, you lose all three effects.

But is a product without added fragrance odorless? Does it contain fewer chemical compounds? Things are not so simple...

In reality, a product that has been removed from its perfume will retain an odor. Less intense, it is not totally absent.

Fragrance-free... but not without smell!

Odors are due to volatile compounds capable of reaching olfactory receptors located in our nose. We have a very high sensitivity to odors and only a few molecules can be detected... An odorous compound in trace amounts will therefore be perceived.

The ingredients used can thus have a smell of their own. We are not talking here about the added perfumes, but about the constituent ingredients of the cosmetic product used: moisturizing agents, fats, surfactants, preservatives, active ingredients... And if the ingredients have a smell, then the cosmetic will also smell. Possibly more annoying, there may be interactions between compounds, generating new scents.

Assessing the intensity of an odour is not easy, and there is no universal measuring instrument. For this reason, the evaluation is usually carried out by... human noses! This type of olfactory analysis can be very subjective, hence the importance of precautions to be considered around the number of evaluators and the rating scale used.

To compensate for differences in sensitivity between individuals, the panel is composed of at least ten volunteers. And to ensure the consistency of their evaluations (a given intensity must be equivalent for all), a series of reference solutions is transmitted to them – usually the n-butanol molecule, naturally present in many foods and with a rather unpleasant odor, diluted in water at several concentrations. The results make it possible to "calibrate", "calibrate" the panel.

We can thus evaluate the intensity of the smell of a perfumed moisturizer, which is on average 8/10. The same cream without added fragrance will have a weaker smell, rated at 2.5/10, which is little... but not zero.

What are the most odorous compounds?

Among the potentially odorous ingredients, we can mention oils and fats that have slight vegetable or nutty odors. Called emollients in cosmetics, they are essential and are found in skin or hair care products because they protect, soften and nourish our tissues.

Their residual odor is due to the presence of compounds commonly found in nature such as oily odor aldehydes, fruity esters or alcohols.

To create an odorless cosmetic product, it would be necessary to use odorless ingredients... that must be created. So we move away from the natural. This is the subject of work in our research laboratory.

Identifying volatile compounds and providing for "targeted remediation" can reduce the smell of emollients: we will seek to eliminate or reduce the presence of specific molecules... But which ones to target? The most abundant?

Again, it's not that simple... Sometimes scarce compounds can have an odorous power: it is therefore they that must be targeted. These chemical elements must then be isolated, identified and quantified. Chemical analyses are associated with sensory analysis because everything is a question, literally, of the nose. Thanks to this work, the residual odor can go from an intensity of 4/10 to 2/10, which is practically undetectable.

Another type of very common ingredient can smell is preservatives, such as phenoxyethanol or parabens. These two synthetic preservatives are pejoratively connoted because they are suspected of being a skin allergen for one and endocrine and reproductive disruptor for the other.

They are allowed in cosmetic products, but their use is restricted and regulated at the level of maximum doses of use. In addition to these potential health effects, however, there are essential ingredients: in particular, they prevent the development of microorganisms in the presence of water, thus guaranteeing adequate preservation over time, even at low doses.

Like oils and fats, they also have a characteristic smell, in this case a rather pleasant floral scent! A pleasant scent is of course not the criterion for selecting a compound. One might think that it is better to choose natural replacements... Except that they are often more odorous than their synthetic counterpart.

We can mention natural vegetable oils (4/10) which have a higher olfactory intensity than synthetic silicones (1/10). These odourless silicones, however, are controversial regarding their environmental and health impacts.

In the end, cosmetics (ingredient and product) without odor, is it possible? Yes, and this is even the case of the most used ingredient in our moisturizers: pure water!

Natural, odorless, fragrance-free: balancing things

"Natural", "fragrance-free", "allergen-free"... As we can see, there are many shortcuts, as are the contradictions that emerge when we seek to minimize the impact of our everyday products on health.

Thus, there is now a desire to move towards ever more odorless cosmetics, which have become a guarantee of quality with the general public – and, therefore, a competitive advantage for ingredient suppliers.

But if we can now reduce the presence of perfume, and therefore allergens, and design bases for neutral creams, this requires the implementation of new purification steps that are sometimes energy-intensive during industrial production!

While the initial residual smell is harmless, without risk...

Scented products remain for the moment the majority in our cupboards and many remain attached to the smell of their shower gel or their body milk. However, there is a desire to move towards ever more natural perfumes.

OUR "COSMETIC" DOSSIER

If the "most natural" has emerged as a selling criterion, it should not be concluded that synthetic ingredients are necessarily "worse" than their natural counterparts. To really judge the harmfulness of a product, it is at the molecular level that we must look – this is the work of research: to identify the molecules at risk, at what concentration, in what environment... And it's still a work in progress!

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This article is produced by The Conversation and hosted by 20 Minutes.

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