Aim, Materials and Methods – Evaluation of the hydrating and elasticizing properties – PRO-YOUTH
AIM OF THE STUDY
The study was carried out to evaluate the moisturizing and elasticizing efficacy, immediate and delayed, of a cosmetic product. In the present research, subjective and objective techniques were used to evaluate the moisturizing and elasticizing effects.
MATERIALS AND METHODS
PRO YOUTH® (INCI Polyglycerin – 6, Aqua, Propanediol, Akebia Quinata Extract, Cimicifuga Racemosa Root Extract, Polygonum Cuspidatum Root Extract, Soy Isoflavones, Angelica Polymorpha Sinensis Root Extract, Trifolium Pratense (Clover) Extract, Pueraria Lobata Root Extract, Kigelia Africana Fruit Extract, Dioscorea Villosa (Wild Yam) Root Extract). The cream tested has the following INCI formula: Aqua, Caprylic / Capric Triglycerides, Ethyl Hexyl Stearate, Glyceryl Stearate, Cetearyl Alcohol, Glycerin, Cetyl Alcohol, Ceteareth-20, Phenoxyethanol, Dimethicone, Citric Acid, Sodium Dehydroacetate, Benzoic Acid, Lecithin, Ethylhexylglycerin, Tocopherol, Ascorbyl Palmitate With 2% Of PRO YOUTH®.
SELECTION OF VOLUNTEERS
For this study, 20 females were selected. The volunteers were recruited according to the following inclusion and exclusion criteria. Inclusion criteria were: between the ages of 20- 65, non-smokers, Caucasians, with normal or dry skin, a negative history of skin diseases, atopy and DAC and for systems or topical treatments in progress; exclusion: pregnant women, lactating women and minors. All subjects were informed about the study procedures and signed an informed consent.
Effectiveness in improving the skin was assessed:
A) instrumentally measuring the degree of hydration , TEWL and elasticity through the sensors of a Multiprobe Adapter System MPA5 of Courage & Khazaka Electronic GmbH (Cologne, Germany);
B) Subjectively, a clinical evaluation was performed by the dermatologist to evaluate tolerability and a self-assessment test on the pleasantness and effectiveness of the tested product.
Evaluation of the cutaneous hydration index
The measurement of skin hydration was evaluated using the internationally recognized Corneometer method. The measurement is based on the evaluation of the dielectric constant of the water. The measuring probe shows changes in the water content of the sample to be measured. A diffuse electric field, generated by the probe head, penetrates the first layers of the skin and determines the dielectricity. The CORNEOMETER® CM825 (Courage + Khazaka, electronic GmbH) has been used for the instrumental evaluation of the hydrating capacity of the products. it allows to measure skin hydration through capacitance measurements between the stratum corneum and the sensor probe of the device. By pressing the front surface of the sensor on the skin, a number appears on the computer monitor: this number is related to the level of hydration on the skin surface. The measurement was performed on a cutaneous area, as flat as possible, taking care to exert a constant pressure for a time set by the instrument itself. The sensor has been kept clean from time to time. A healthy skin in conditions of about 20 ° C of temperature and about 40-60% of environmental humidity should, in the monitored region, have a hydration index> 45.
Evaluation of cutaneous elasticity
The cutaneous elasticity was evaluated using the suction / elongation method and the subsequent release of the skin inside a measuring probe. During the suction / elongation phase the instrument generates a constant negative pressure able to suck the skin inside the probe. This is followed by a release phase, in which the pressure inside the probe is brought to zero millibar thus allowing the skin to return to a state of rest. An optical detection system evaluates the depth reached by the skin inside the probe during the two measurement phases. The computerized suction instrument, equipped with a 2 mm probe, used by us was the CUTOMETER MPA580® (Courage + Khazaka Electronic GmbH, Köln, Germany). Before the test, it was necessary to proceed to the setting of the measurement technique, of the depression level and time, of the subsequent release time and of the number of successive measurements on the same test area. In this case it was considered appropriate to choose the measurement technique which provided, at a standard pressure of 450 mBar, a depression which steadily increased in a time of 10 seconds and an equally constant release in the same period of time, for 5 successive measurements.
This choice is motivated by the fact that, by applying weakly weak suction forces, it is possible to investigate the elasticity of the epidermal layers and the superficial dermis, ie the cutaneous areas that can be most affected by a cosmetic treatment.
Figure 1 shows graphically the behavior of the skin in the suction / elongation phase (from 0 to 5 seconds) and then in the release phase (from 5 to 10 seconds). As you can see from the figure the skin reacts to the negative pressure stimulus with a biphasic type response characterized by a first phase of rapid relaxation (Ue) followed by a second phase in which the skin tends to oppose the stimulus (Uv) reaching its maximum degree of deformation (Uf). In literature the first part of the curve is known as the elastic component of the skin while the second part characterizes the viscoelastic component, represented for the most part by the plastic component. Analogous is the behavior of the skin at the end of the negative pressure stimulus in the release phase. In fact, if in a first phase (Ur) the skin tends to return to its original state of rest, given its elastic qualities, in a second phase the plastic component exceeds the elastic one, slowing down the speed of redefining the skin (Ua-Ur) up to keep the skin in a deformed state (Uf-Ua); this phenomenon is known as hysteresis. The skin deformation curves were analyzed using the Win-Cutometer MPA software which provided the parameters listed in Figure 1. These skin parameters were divided into two main categories: elastic and viscoelastic and further subdivided into absolute and relative.
Absolute parameters are: Ue, Uv, Uf, Ur, R8 (Ua) and R0 (Ue + Uv), R1 (Uf-Ua).
Relative parameters are: R2 (Ua / Uf), R5 (Ur / Ue), R6 (Uv / Ue) and R7 (Ur / Uf).
The absolute parameters are measured in millimeters, while the relative parameters are presented with a number, which represents a ratio between the values of two absolute parameters – whose maximum value is 1 ( 100%.) Absolute parameters are believed to depend on the thickness of the skin, which varies with age, gender and body region. This is the reason why in comparative studies, the thickness of the skin must first be standardized with ultrasound. Since this is not always possible, it is preferable to use, in comparisons, the relationships between absolute parameters, ie the relative parameters. It is admitted that these do not depend on the thickness of the skin and can be compared between subjects and anatomical regions (Berndt 2002). The reason is that the relative parameters are composed of two parts: the numerator and the denominator, and the same value can be the result of an increase of the numerator or a decrease of a denominator and vice versa (Dobrev 2000, Dobrev 2002). their biological information the R parameters are divided into three groups (Barel 1998, Dobrev 2000, Dobrev 2002): Absolute elastic parameters [Ue, Uf and Ur] and related Elastic Parameters [R2 (Ua / Uf), R5 (Ur / Ue) and R7 (Ur / Uf)]; Absolute viscoelastic parameters [Uv and H] and related Viscoelastic Parameters – Uv / Ue; Mixed parameters [R1 and R4]. In the present study the mechanical parameters used are some of the most recommended to characterize the main mechanical properties of the skin: Ue and Uf (distensibility), Ue / Uf and Ur / Uf (elasticity) and Uv and Uv / Ue (viscoelasticity) (Dobrev 2000, Dobrev 2002). The distensibility of the skin is the ability of the skin to undergo stress or it can be understood as the resistance of the skin to change shape under the influence of stress. The elasticity of the skin is the ability of the skin to recover the original shape after a deformation. The viscoelasticity of the skin is the time-dependent deformation with a non-linear phenomenon of “plastic sliding” and “hysteresis”. Description of the parameters used: R0 (absolute parameter) is called final distension or skin distensibility and is the highest point of the first curve (Uf). This parameter evaluates the solidity (firmness, rigidity) of the skin. It represents the passive behavior of the skin to external forces and is an absolute parameter that depends on the thickness of the skin: if it increases, in its components, its flexibility is reduced (Jachowicz 2008). The more the value tends to the more elastic the skin will be. In fact, the decrease of R0 represents an increase in the thickness of the skin and the corneous state and / or an increase in thickness or a decrease in the length of the collagen fibers that cause a skin stiffness. The skin stiffness can be reduced with the help of emollients.
In this way the tension between the stratum corneum and the epidermis is felt and the underlying dermis is diminished as the lines and wrinkles of the skin are smoothed. A decrease in R0 may also be due to a firming effect induced by a cosmetic product capable of producing changes in the properties of the skin inducing a greater skin tension (Dobrev 1998) .R6 (relative parameter) represents the relationship between viscoelasticity and distension elastic ie Uv / Ue. It is the portion of visco-elasticity on the elastic part of the first curve. Indicates the relative contribution of viscoelasticity to elastic deformation of the skin. The lower the value, the greater the elastic distension; the greater the value, the greater the viscoelasticity. This parameter is the most indicative of the epidermal and dermal water content (Dobrev 2000), this because the mechanical properties of the skin are influenced by the level of skin hydration. The increase in R6 can be the consequence: a) at the dermal level of a decrease in interstitial viscosity, as a result of an increase in water content and changes in the composition of proteoglycans, the accumulation of water in the dermis in fact decreases the friction between the fibers and facilitating the movement of the interstitial fluid attributed to the movement of interstitial fluid through the dermal fibrous web (Hashmi 2007, Jachowicz 2008); b) at the epidermal level of a softening, with increased plasticity, of the stratum corneum as a consequence of the increase in it of the water (Ryu 2008). To confirm this, a study showed a decrease in the R6 and R5 parameters in the skin slightly dehydrated by the use of an alkaline soap (Maia Campos 2008) and another work showed a positive correlation between epidermal hydration and the Uv and R6 parameters (Dobrev 2000). R7 (relative parameter) or biological elasticity (Paye 2007). It is the portion of elasticity compared to the final distension. It represents the relationship between the immediate retraction and the final distension ie Ur / Uf (Dobrev 2000). The more the value is close to 1 (100%) the more the skin is elastic. R7 is independent of the thickness of the skin, measuring the ability of the skin to recover its initial position after deformation. R7 together with R2 is used as the main parameter to evaluate the elasticity and aging of the skin (Ahn 2007).
Evaluation of the evaporation of the epidermal water (TEWL)
The index of evaporation of water from the epidermis (TEWL) of the skin The treated skin area was measured using the TEWAMETER® TM300. The skin constantly loses water in the form of steam and TEWL is the most important parameter to evaluate the efficiency of the water barrier function of the skin. The measurement of water evaporation is based on the principle of diffusion in an open chamber and the physical basis of measurement is the law of diffusion discovered by Adolf Fick in 1855. This tool allows to evaluate the flow of water vapor through a specific unit of surface by changes in water concentration and temperature in the atmosphere near the stratum corneum. The measuring probe is a shallow cylinder (diameter 10 mm and 20 mm length) in order to minimize the influences due to air turbulence inside the probe. It consists of two pairs of sensors that measure humidity and temperature gradients in two different distances. After detecting the resulting humidity and temperature gradients, the TEWL is automatically calculated and shown on the computer monitor.
An in vivo blind single-blind trial was performed. The active cream was applied according to its characteristics of use, twice a day on the skin. Its efficacy was assessed in both the short and long term tests, which lasted 30 days. The area used for the instrumental tests was the fly region of the forearm. On the forearm the surface to be analyzed was delimited with a surgical tape on which a square cut was made, with an area of 6 cm2 that remained in place for the entire short term test and was reapplied during the long term measurements test.
The corneometric measurements were four for each area in the medium-lateral direction. Elasticity and TEWL were evaluated with a single measurement in the center of the square. The tolerability and efficacy of the products was evaluated by the dermatologist and by the patients themselves observed the skin of the body. Instrumental evaluations were performed at time t0 (baseline value), after 1 hour (t1h) and 24 hours (t24h) in the short term test and after 15 days (t15d) and 30 days (t30d) of continued application of the product in the long term test. Before every measurement, every volunteer remained for 30 minutes uncovered forearms, to acclimatize the skin to temperature and humidity the air-conditioned room in which the tests were carried out. Before the t0 each volunteer was asked not to clean the forearm, for at least 3 hours before the experiment.
After this period the baseline values of corneometry were measured. If, after the acclimatization phase, at least two very different hydration values were observed (greater than ± 5 corneometric units), more time was expected before proceeding with instrumental evaluations. The volunteers who, even after this precaution, still showed differences in constant reading and above ± 5 u.c., were discarded. Following the hydration measurements, the cutometric measurements, the evaporimetric measurements and the clinical evaluations were carried out. After the basal hydration, elasticity and TEWL values were measured, the product was applied to the subjects to perform the short term test. After 24 hours, at the end of the short term test the product was delivered for the long term test.
EVALUATION OF TOLERABILITY
For the evaluation of tolerability were recorded all the undesirable local events, immediate or delayed, occurred during the study, evaluating the severity, the time of onset, duration and possible relationship with the treatment.
To evaluate the cosmetic properties of the cream and its action on the skin has been prepared a psycho-psychological test. The questionnaire asked questions about the efficacy of the product and the score was graded as: “for nothing”, “poor”, “indifferent”, “quite” and “very”.
All results were compared with the baseline measurement at any time, using Student’s t- test for paired data or a non-parametric test (Wilcoxon signed rank test) when the difference in averages did not show the characters of normalcy verified using the Shapiro- Wilk test. The results were considered significant if p <0.05 (95% Confidence Level) and were calculated using a Microsoft® Excel spreadsheet. All data were presented as mean ± standard deviation and in addition to the measured value they were also reported as differences vs basal (difference and percentage value).