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dermatology

Under the skin

Beauty creams stimulate more brain regions in women with sensitive skin

L'ORÉALIrritation on the skin: activating different areas of the cortex in women with sensitive skinL'ORÉAL

There is no doubt that the skin of two individuals can react – and react effectively – in a different manner to the application of a cream or beauty product. Some people use enormous quantities of a cosmetic without showing any form of skin irritation. Others, just after having put the same product on their skin, feel itching or burning at the point where they applied it. Might looking at what is happening in the brain of individuals with sensitive skin and those with non-sensitive skin, help to better understand the problem? Perhaps, if one judges by the results of a recent survey. In collaboration with the National Health and Medical research Institute (Inserm in the Portuguese acronym) and the Bicêtre Hospital in Paris, researchers with the company L’Oreal, the French multinational in the cosmetics area, have demonstrated that, on entering into contact with substances known to be irritants, women with skin classified as sensitive show a standard of brain activity very different from those who have a skin that is not sensitive.

With the help of images obtained through a technique of functional magnetic resonance, capable of showing which sectors of the brain are activated by a stimulant, the authors of the study realized that the areas activated among women with sensitive skin were in greater number and distributed themselves in a manner more or less uniform between the two hemispheres. With the participants with non-sensitive skin, the answer was much more discrete and mostly concentrated in the hemisphere opposite the region of the body to where the stimulus has occurred. “We have the impression that the information (referring to dermal discomfort) arrives at the brain of all women in the same manner, but is dealt with in a different way according to the context, to the sensitivity of the skin”, explains the French physicist Bernard Querleux, the main author of the work and L’Oreal’s research director, who was in Brazil last month. Part of this study was presented at the 20th World Conference of Dermatology, which took place in Paris last year.

The brain’s responses
In his studies, Querleux and his assistants set out to determine, in an objective manner, the neural bases of sensitive skin. It is an important line of research for the cosmetics industry, products of which are placed over the epidermis and must beautify their consumers – and not cause them pain or discomfort. In Europe and the United States, half of the women, the main consumer public for face creams, have skin that is more susceptible to showing undesirable reactions after the application of a cosmetic. In China, one third suffer from the same problem.

In other parts of the world, at least 10% of the female population have this characteristic, according to data from L’Oreal, which invests 3% of its yearly revenues (something around half a billion Euros) in their research division. To have sensitive skin is not a rare condition, but to diagnose the problem is not always easy starting from clinical signs or from biophysical measures. “This is a theme that still carries with it a large dose of subjectivity”, Querleux comments, “hence our interest in studying it.”

In order to see how the brain reacts when confronted with a product that is more aggressive to the epidermis, the French researchers carried out an experiment with eighteen women, of whom half said that they had sensitive skin. On the left hand side of the face they placed droplets of an inert solution and applied to the right lactic acid, a substance normally used as an irritant in tests on dermal reactivity. During a ten-minute period the magnetic resonance device registered the functioning of the brain of each of the women. This type of equipment measures changes in the flow of blood and oxygen in the regions where there is a large amount of neuronal activity and generates images in which the brain areas brought into action by the stimulus are highlighted. At the end of the experiment, even before analyzing the magnetic resonance images, the scientists had already managed to easily separate the women into two groups.

Those who showed greater discomfort on the right face where the lactic acid had been applied made up part of the group previously labeled with sensitive skin. Those who showed less irritation on this side of their face were in the team of non-sensitive.Up until this point the study appeared to confirm the obvious: those who declared themselves to have sensitive skin suffered more from the effects of the irritant substance.

The work became more original when Querleux and his colleagues went on to evaluate the profile of the brain activation of the two groups of women. There were some common points and evident differences. Among the points in common that came up, there was the realization that all of the patients, with or without skin sensitivity, had shown an increase in neuronal activity in the primary sensorial cortex of the left hemisphere of the brain. The cortex is the gray mass that forms the most external layer of the brain, and is responsible for the control and integration of voluntary movements and of feelings and has nerve centers linked to memory, language, thought and intellect.

Therefore, in the patients whose right face had been exposed to a substance that causes discomfort, the registration of neuronal activity on the left of the cortex was greater than that expected. In the end, the left hemisphere directs and feels the right side of the body and vice-versa. In the chapter dealing with the differences between the two groups of participants in the study, more interesting data came up. In spite of the facial irritation having led all of the women to react, in both of the brain hemispheres, at two subdivisions of the cortex (the pre-frontal and cingulate regions) the neuronal activity registered in these subdivisions was much greater in those with sensitive skin, especially in the right side of their brain.

This data led Querleux and his colleagues to think that the pre-frontal and cingulate cortexes could be directly linked to greater sensitivity of the skin. “We cannot forget that to have sensitive skin is to feel the lowermost level of pain, on a nano-metric scale, because of the application of a cosmetic”, says L’Oreal’s research director. “For this reason, the neuronal circuits of sensitive skin can also be looked upon as circuits of pain”, Querleux concludes.

Besides studying the neural bases of sensitive skin, the researchers at the cosmetics multinational developed studies destined towards increasing their understanding about touch. In another study done with the help of functional magnetic resonance, they gathered evidence that neuronal stimulus brought about by the application of a cream in the hand of a woman seems to vary according to a basic trait of her personality.

After making use of the product, the most imaginative bring into intensive action both of the brain hemispheres. In the case of more objective and logical women, the cerebral activity tends to concentrate in the hemisphere opposite to the hand that received the cosmetic. For L’Oreal, the study is providing clues about what a cream might do to the most emotive portion of the brain of people, above all those who are most sensitive.

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