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Print version ISSN 0365-0596On-line version ISSN 1806-4841
An. Bras. Dermatol. vol.77 no.5 Rio de Janeiro Sept./Oct. 2002
CLINICAL, LABORATORY AND THERAPEUTIC INVESTIGATION
Study of pH variation on the skin using cosmetic formulation s with and without vitamins A, E or ceramide: by a non-invasive method*
Gislaine Ricci LeonardiI; Lorena Rigo GasparII; Patrícia M. B. G. Maia CamposIII
Masters and Ph.D., FCFRP-USP, Professor of the Pharmacy Course and Coordinator
of the Cosmetology Specialization and Manipulation Magisterial at the Methodist
University of Piracicaba - UNIMEP
IIPharmacist, FCFRP-USP, Masters and Ph.D., FCFRP-USP
IIIPharmacist - FCFRP-USP, Masters and Ph.D. - FCF-USP and Professor of Cosmetology at FCFRP-USP
Moisturizers are believed to improve the skin's condition by increasing the
water content of the stratum corneum. Vitamins A and E and ceramides have been
widely used in cosmetic moisturizing products, and these are one of the most
important cosmetic and body care products.
OBJECTIVE: The aim of this research was to evaluate the effects on the pH of human skin of an O/W emulsion (non ionic self-emulsifying base) with and without vitamin A palmitate, or vitamin E acetate, or ceramide III, using a non-invasive method.
METHOD: The investigations were carried out on a group of 40 healthy female test subjects aged between 30 and 45 years old, using the Skin pH meter PH 900 PC. The measurements were performed on the forearm of volunteers at 7 and 30 days after daily use (twice a day) of the products used in the study.
RESULTS AND CONCLUSION: The presence of vitamins A or E or ceramide III did not change the pH of the skin, consequently the formulations studied are suitable for cosmetic usage.
Key words: lipids; vitamin A; vitamin E.
Moisturizers constitute one of the most important classes of cosmetic and body hygiene products since they are widely used for both preventative action (against xeroderma and in the retardation of precocious aging) as well as for their usefulness in supporting dermatological therapeutics in a considerable variety of cutaneous dysfunctions.1
The addition of active substances into many cosmetic formulations used to moisturize skin has become a very frequent practice.
The use of ceramides in cosmetic products has also been growing recently since the endogenous ceramides, which are part of the lipid mantle of the skin, act by retaining water in the corneum stratum and thereby helping to maintain the skin hydrated.2-7
Among other active substances much used in skin care today, are vitamins A and E.8-12 Vitamin E has stood out in anti-aging formulations, because, besides its humectant property, it is also a potent neutralizer of free radicals.13 Likewise, vitamin A has been reported as an activate substance for anti-aging purposes.14-15
Demonstration of the effectiveness of the active substances used in cosmetic products, as well as the effects caused by the formulations in human skin, have been the subject of study among the scientific community. Such research results in technical and scientific progress within the cosmetic sector that is developing more and more and winning space in this epoch in which quality of life has become a major objective.
Research into cosmetology has been growing more and more, due to the contribution and partnership of several areas of the basic and applied sciences, including pharmacology, dermatology, histology, anatomy, physiology, microbiology, chemistry and physics.16
In the last few decades we have witnessed an explosion of information and scientific progresses related to cutaneous research, which has benefited both dermatologists and professionals that work with the development of cosmetic products.17-18
Before the use of noninvasive techniques, dermatology and similar areas were based, essentially, on clinical observation alone, which due to its subjective nature could be considered a somewhat imprecise method. However, following technological progress the noninvasive methodologies have appeared, which are scientifically proven and non traumatic, without involving any aggression or discomfort to either patients or volunteers participating in the studies. The application of these methodologies has been revolutionizing the cosmetic sector, since they have enabled a quantitative analysis and better still have scientifically demonstrated the beneficial effects of the cosmetic products.18
In the last twenty years, equipment offering a wide application (for cosmetology, aesthetic medicine and dermatology) has become available, thus giving rise to new noninvasive methodologies for cutaneous research.19-33
An example of such apparatus is the Phmeter", which evaluates the superficial pH of the skin.
The determination of the pH of the cutaneous surface, or that is the hydrogen ionic concentration, has been the subject of much research. The pH of the cutaneous surface is seen by some authors as an important functional indicator of the skin, since it arises from the production of lactic acid which confers the so-called "cutaneous acid mantle".34
Healthy skin presents a slightly acid pH (4.6 - 5.8), which contributes to the bactericidal and fungicidal protection of its surface. Furthermore, the cutaneous secretions present an appreciable buffering capacity; an important property since the pH of the skin is frequently altered as a consequence of the use of inappropriate topical products, thereby exposing the skin to a series of aggressive agents and especially microorganisms.35-37
Hence, determination and control of cutaneous pH, from the cosmetic and/or dermatological point of view, are of extreme usefulness since contact with aggressive substances, such as detergents can be frequent and also in order to avoid the use of inadequate topical products.35
Regarding the techniques developed for pH determination, measurements using a potentiometer have gained a particular emphasis, this is performed with several types of electrode: hydrogen, quinhydrone and antimony.18With the Phmeter", analysis of the pH of the cutaneous surface is made by direct potentiometry, or that is, through a special electrode.36
Direct potentiometry has been the method of choice for measurement of this variable and allows sensitivity in the order of 0.1 of the pH unit.37
In view of the above, the objective of this work was to evaluate the effect on the cutaneous pH of human skin of O/A emulsions with and without the addition of vitamin A palmitate, vitamin E acetate or ceramide III, using noninvasive methodology.
For this study an O/A emulsion was used comprising: 17% nonionic self-emulsifying wax; 3% squalene; 0.5% imidazolydinyl urea; 0.2% methylparaben; 0.1% propylparaben; 10% glycerin; 0.3% glutathione; 0.04% DL-alpha tocopherol; and distilled water. This formulation (considered to be the vehicle) was tested with and without the addition of vitamin A palmitate (5,000UI/g) or vitamin E acetate (20mg/g) or ceramide III (1mg/g).
Evaluation of cutaneous pH
The study protocol was approved by Committee of Ethics in Research of the Hospital das Clínicas, Faculty of Medicine of Ribeirão Preto, University of São Paulo (FMRP-USP) and was conducted in 40 women after informed consent, with age ranging from 30 to 45 years and skin type II, III or IV.
The volunteers that participated were neither using medication nor presented dyschromia at the time of the study. Having read and understood the Term of Informed Consent, they declared that they fully agreed in participating in the research and were aware of the procedures, risks and benefits, among other related factors.
The study was performed using Skin pH meter PH 900 PC apparatus, which measures the cutaneous pH. The measurements were taken in the volunteers' forearm, on day seven and 30 after self-application (twice a day) of the products in question. The application area was duly cleaned with distilled water and cotton and, shortly afterwards, dried with a paper towel 30 minutes before the reading.
To determine the pH of the corneum stratum three measurements were made at the study venue and the results were presented as mean values of these sequential measurements.
The volunteers' left forearm was treated with the various formulations. The 40 volunteers were divided into five groups of eight women each. Group 1 used a formulation without any active substances (or in other words, only the vehicle selected for evaluation). The remainder used this vehicle with several substances added: Group 2, 0.5% vitamin A palmitate; Group 3, 2% vitamin E acetate; Group 4, 0.1% ceramide III, and finally the Control Group which used nothing on the skin.
A fixed quantity of the sample was applied to the skin of the volunteer's forearm and distributed in circular movements for 15 seconds.
The entire test was conducted in a room with controlled temperature (between 20 and 22°C) and relative humidity (50 to 60%).
The study was performed using a statistical software package (GMC program) elaborated by Maia Campos,39 and the results statistically analyzed by variance analysis.
RESULTS AND DISCUSSION
The results of the cutaneous pH for the different formulations used in the study are summarized in table 1.
The results of the preliminary tests indicated that the sample was reasonably homogeneous and the distribution of frequencies was very close to the distribution of frequencies of the normal mathematics, which indicated the use of parametric statistics in the data analysis.
The most appropriate parametric test for the mathematical model of this experiment was variance analysis and since this was a mixed model, in which a factor with independent variation was at the same time associated to a linked factor, variance analysis using the partition data technique was employed.
The results of the test for variance analysis are shown in table 2.
As can be seen in table 2, the variance analysis demonstrated that there was no statistically significant difference in the cutaneous pH in relation to the time periods studied in this work. It can be concluded, therefore, that the time factor did not influence the pH of the human skin. The statistical analysis also demonstrated no statistically significant difference in the pH of the skin when comparing the formulation (vehicle) and addition of the active substances involved in the study.
From the above results, it was verified that there was no statistically significant difference between the factors studied (time, active substance, presence or not of active substance in the vehicle). In other words, the presence or absence of the various active substances studied (vitamin A palmitate, vitamin E acetate and ceramide III) in the cosmetic vehicle and in the time periods analyzed, did not cause a significant alteration in the pH of the skin, thereby demonstrating that the formulations studied are appropriate for cosmetic usage.
The authors extend their thanks to Prof, Dr Ana Maria Ferreira Roselino, M.D. dermatologist at FMRP-USP, for her valuable suggestions.
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Profa Dra. Gislaine Ricci Leonardi
Rua Floriano Peixoto 1630 ap101
Piracicaba SP 13400 520
Tel.: (19) 3434-1537
Received in August,
31th of 2001.
Approved by the Consultive Council and accepted for publication in April, 16th of 2002.
*Work done at "Faculdade de Ciências Farmacêuticas de Ribeirão Preto da Universidade de São Paulo"