THE ASYMMETRY OF THE FACE MAKES IT POSSIBLE TO QUANTIFY THE PHOTOAGING DUE TO ULTRAVIOLET RADIATION
Pr Philippe Humbert
This study highlights the role of photoaging and predominantly lateral ultraviolet exposure as determinants of facial asymmetry. Photoaging is a phenotype of an individual that is considered to be the part of aging related to solar irradiation, which can be summarized as ultraviolet irradiation if infrared is ignored.
More than an appearance, photoaging is also histo-pathological disorders such as dystrophic elastic fibers, reduction of collagen content in skin tissue and increase in the activity of prosthetic enzymes such as metalloprotease1 (MMP1). UVA has the ability to modify skin cells in culture but also in vivo.
Thus, for the first time, we have been able to quantify in terms of additional age the part of aging due to exposure to ultraviolet rays. This part of aging, which is called photo-aging, is on average six years, for 30 years of exposure (number of years of professional activity).
Thus, every five years, each individual can be considered to age an additional year due to sun exposure. These findings provide important support for recommendations on photo-protection by any means.
The author concludes this work by insisting on the implementation of appropriate preventive and curative methods, both topical and oral, with the administration of nutrients and food supplements with antioxidant properties.
Keywords: photoaging, face, asymmetry, ultraviolet radiation, uVA, biometrology, prevention, treatment.
THE HUMAN BODY IS NOT SYMMETRICAL
It has always been noticed that the human body, despite its great perfection, is not symmetrical.
Seen from the outside, symmetry seems to be one of the characteristics of this body made of even parts (limbs...) and odd parts (face...).
However it would have been observed that the breasts of a woman are not completely superimposable, that the scrotum in the man that the sculptors perfectly noticed (michel-Ange) was constituted of a purse lower on the left. These are the most remarkable elements.
Inside the body, the asymmetry is even greater. The lungs have three lobes on the right and two lobes on the left. The stomach is not median but shifted to the left etc.
As for the face, since we take particular care to analyze it, we have noticed how asymmetrical it is. This has been the subject of several medical publications on "clinical cases".
Here is the case of a teacher, a patient of Professor Moulin, showing the left side of her face exposed to the sun for many years.
PHOTOAGING OF THE FACE DUE TO ULTRAVIOLET RADIATION
The ultraviolet radiation to which the globe is subjected includes:
Ultraviolet b (280-315 nm),
Ultraviolet A (315-400 nm),
Ultraviolet C (100-280 nm), totally absorbed in the atmosphere. During a summer day :
About 3.5 % of the ultraviolet irradiation reaching the earth is UVB,
While 96.5 % represent UVA.
Ultraviolet b is almost entirely absorbed by the glass, while almost half of the UVA passes through it.
Although 1,000 times less energetic than UVB photons, UVA photons are capable of inducing age-related changes, even deep in the dermis, due to their great capacity to penetrate the skin deeply.
Photoaging is a phenotype of an individual that is considered to be the part of aging related to solar irradiation, which can be summarized as ultraviolet irradiation if infrared is ignored.
In any case, this was what prevailed in recent years since the role of infrared was underestimated.
If we look at the aging of a person who has been exposed to intense heat throughout his or her working life (this is the case for people working in front of boilers, ovens, fireplaces, especially in ironwork), we cannot ignore the role of this heat in skin aging.
WHAT IS THE ROLE OF UVA ON FACIAL AGING?
More than an appearance, photoaging is mostly histopathological disorders such as :
Dystrophic elastic fibers,
The reduction of the collagen content of skin tissue
And the increase in the activity of prosthetic enzymes such as metalloprotease1 (mmP1). UVA has the ability to modify skin cells in culture but also in vivo.
These effects are due to reactive oxygen species generated through endogenous chromophores such as transurocanic acid and porphyrins which act as photosensitizers. This oxidative stress leads to damage of structural proteins, lipids and DNA, especially since we observe in parallel, the reduction of these key enzymes in the purification of free radicals, which are catalase and superoxide dismutase (SOD).
THE LEFT SIDE OF THE FACE IS THE MOST EXPOSED TO UV
It has been recognized for several years that the left side of a face has been more exposed than the right side for the last 100 years, since it is closer to the car window when it is the driver's face. The researchers also studied twin pairs with different lifestyles between individuals.
These studies make it possible to avoid inter-individual variability. But as Professor Moulin demonstrated, this photoaging, which was more marked on the left (in the case of the teacher whose case he reported), could have been more important on the right, if she had taught in a room with a window on the right side.
THE CLINICAL AND BIOMETROLOGICAL STUDY ON FACIAL ASYMMETRY THAT QUANTIFIES PHOTOAGING DUE TO UVA 
The author's team (University of Franche-Comté) carried out an original clinical study under the direction of Mac-Mary S. [2, 4] using people who had noticed some asymmetry in their face. A wide variety of "responders" were interviewed. Each had professional activities that could be considered responsible for the asymmetry. The trades involved were represented by drivers, teachers, sales clerks, sales representativesOn this basis a bio-metrological study was conducted to try to determine the amount of radiation needed to observe the role of photoaging in the aging of the individual.
10 people were selected, 8 women of 65 years old on average and 2 men of 60 years old on average, living in the east of France, who all had a job related to driving. They were therefore subjected almost exclusively to additional UVA irradiation on the left side of their face.
Thus, clinical scores for cheek wrinkles, eye contour, crow's feet, and laxity measures were rated more severely on the left.
Curiously, less heterogeneity in skin color was observed on the more exposed side.
Wrinkles had a greater volume and skin roughness in the exposed half of the face.
RESULTS: THIS STUDY SHOWED THE STRONG IMPACT OF THE CUMULATIVE EXPOSURE OF THE SKIN OF THE FACE TO UVA
Since Lowe's work, it is known that even repeated non-erythematous doses of UVA can induce photoaging. This results in thickening of the epidermis and deposits of lysozyme in the elastic fibers. Using software, this study created two new faces for each volunteer:
One of them consists of two times the most affected hemiface, i.e. the left hemiface
And for the other, a face made up of two times the right hemiface.
Thus for each volunteer there were two faces that could represent two different people, one appearing significantly older than the other.
By randomly presenting these faces to a panel of 98 experts, it was observed that the apparent age of the hemi-face reconstructed from the left half of the face appeared five to seven years older than the other.
Thus, for the first time, we have been able to quantify in terms of additional age, the proportion of aging due to exposure to ultraviolet radiation. This part of the aging process, which is called photoaging, is on average six years for every 30 years of exposure (number of years of professional activity). Thus, every five years, each individual can be considered to age one additional year due to sun exposure.
PREVENTION OF THE MULTIPLE EFFECTS OF EXPOSURE TO SOLAR RADIATION
These findings provide important support for recommendations on photoprotection by any means.
Because sun exposure is not only ageing, but also other losses of skin functions:
Like the mechanical functions,
And the protective functions against the development of cancers.
This is why it is important to consider that with age, the skin is depleted of anti-radical factors, i.e. antioxidant factors:
Such as endogenous antioxidants: catalase, SOD,
And exogenous antioxidants: trace elements, vitamin C.
PREVENTIVE TREATMENTS FOR PHOTOAGING OF THE FACE
If we consider that the main antioxidant of exogenous origin is vitamin C, it is necessary to know the results of this study published in 2003 quantified the content of vitamin C in the dermis and was able to demonstrate that at 60 years, the quantities of vitamin C in the skin were half of those at 20 years (and it was not only in the photo-exposed skin)
Antioxidant of the body, thevitamin C is the main factor ofIt is therefore important to provide the skin with systemic and topical vitamin C in a form that is not oxidizable and that has proven its transcutaneous penetration. The same applies to the essential need for Super Oxide Dismutase (SOD), given the widely demonstrated need for SOD during aging and the importance of Glisodine [4, 5].
In aesthetic medicine, the role of photoaging and ultraviolet exposure as a determining factor of facial asymmetry cannot be ignored.
Therefore, appropriate preventive and curative methods, both topical and oral, should be implemented and the administration of nutrients and dietary supplements, whose evidence of antioxidant properties is based on research, should be advised [4, 5].
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