In vivo and in vitro evaluation of topical formulations containing physiological lipid mixture for replacement of skin barrier function.

AIM: The aim of the study was to describe a new in vivo and in vitro approach of the efficacy evaluation of cosmetic emollients to better understand the link between the formulation and the activity of cosmetic products. METHODS: Two long term in vivo studies were carried out on nine healthy Caucasian volunteers mean age 40±12 years to evaluate the protecting and repairing effects of the two different barrier repair cosmetic formulations. The application of the formulations was repeated once a day during 7 days and biophysical parameters (TEWL and Skin Hydration) were measured before and after Sodium laureth sulphate exposure The in vitro study was carried out by freeze substitution transmission electron microscopy (FSTEM) on stratum corneum samples obtained by sections of fresh skin from young pigs, depleted with a solvent mixture and treated with the two products RESULTS: The in vivo results demonstrated that daily product application provided a reinforcement of the skin barrier with protecting and repairing effects from chemical injuries the extent of which was dependent on the formulation features (product A>product B) The role of the technical form on the lipid availability was confirmed by the in vitro evaluation tests. CONCLUSION: The results point out that a daily application of physiological lipid mixture containing emulsion can protect healthy skin and promote the reparing effect on unpaired barrier skin, reducing TEWL and maintaining hydration of the stratum corneum. The efficacy degree is higher when the cosmetic form promotes the availability of active ingredients increasing the product performance.

Stability of vitamin C derivatives in solution and topical formulations.

The stability of ascorbic acid, ascorbyl palmitate and magnesium ascorbyl phosphate (VC-PMG) in both standard solutions and topical formulations was investigated by direct RP-HPLC analysis after sample dilution with a suitable aqueous-organic solvent mixture. The results showed that, whereas the two vitamin C derivatives were more stable than ascorbic acid, the ascorbyl esters showed significant differences. Esterification with palmitic acid in 6 position did not prevent hydrolysis of the molecule, either in solution or in emulsion; only the special preparation of products with high viscoelastic properties was able to reduce the typical behaviour of this compound. Conversely, the introduction of the phosphoric group in 2 position protected the molecule from break-up of the enediol system, confirming VC-PMG as a very stable derivative of vitamin C that may be easily used in various types of cosmetic products.

Chemico-physical and functional properties of inorganic sunscreens in cosmetic products.

Synopsis This paper reports preliminary results of a study carried out on liquid crystal emulsions added to three different inorganic sunscreens: ultrafine zinc oxide, ultrafine titanium dioxide (inorganic-treated) and ultrafine titanium dioxide (organic-treated hydrophobically). The aim of the work was to investigate the influence of chemico-physical properties of inorganic sunscreens on the microstructure of cosmetic emulsions. The study was carried out using three different techniques: rheological measurements performed in dynamic conditions, to study the homogeneity of samples and their structural features; dispersion of powders in emulsions by optical microscopy and SEM/EDX analysis; and functionality of emulsions by UV spectroscopy, with adhesive tape as substrate. Results show that the different chemico-physical properties of the micropigments lead to different interactions with emulsion components; these interactions may affect the functionality and microstructure of the whole system, with loss of stability.

Stability of vitamin A palmitate in cosmetic emulsions: influence of physical parameters.

Synopsis The aim of this work was to verify if a close relationship exists between the physical stability of an emulsion and the chemical stability of vitamin A palmitate included in it. Oil-in-water cosmetic emulsions with high viscoelastic properties were prepared, and their rheological behaviour was investigated in oscillatory conditions. The stability of each sample was verified in high-temperature stress conditions: periodical checks of physical parameters and chromatographic analysis of vitamin A were performed during storage. Results show that the chemical stability of vitamin A palmitate strictly depends on the physical stability of the formulation and in particular on the presence of a coherent gel-like structure in the external phase of the emulsion.

Controlled release of dehydroacetic acid sodium salt for the stability improvement of cosmetic formulations*.

Synopsis The kinetics of decomposition of the sodium salt of dehydroacetic acid (DHA.Na) in presence of formaldehyde and formaldehyde donors was investigated. The possibility of preparing systems capable of providing the cosmetic preparation with increasing amounts of DHA.Na corresponding to portions interacted with formaldehyde was explored. Data relevant to matrices prepared from ethylcellulose and polyethylene by casting and moulding process, respectively, are reported and discussed. Experimental data demonstrate the possibility of preparing polymeric systems able to control in terms of rate and duration the relase of DHA.Na, according to time and concentration needs of a typical cosmetic formulation.

Rapid pentachlorophenol evaluation in solid matrixes by second derivative UV spectroscopy for application to wood and leather samples.

A method for the quail-quantitative evaluation of pentachlorophenol (PCP) in solid matrixes has been developed. The procedure is based on solid-liquid extraction of solid samples (leather or wood), followed by purification on a cyanopropyl column and determination of the preservative by second derivative UV spectroscopy considering the PCP A peak-through value (304-297 nm). The method allows rapid PCP determination in the concentration range 1-40 micrograms/mL; any matrix interference is avoided by the purification step and recoveries of the preservative were 99.12% (RSD% 0.13) for the leather matrix and 98.03 (RSD% 0.17) for the wood matrix.

Dowicil 200 Stability test: chemical and microbiological studies.

Synopsis The stability of the formaldehyde-releaser preservative Dowicil 200 has been investigated. The studies were carried out on cosmetic emulsions preserved with different concentrations of Dowicil 200, stored in the dark at 45 degrees C or 25 degrees C. The degree of microbiological activity was tested with respect to S. aureus, P. aeruginosa, E. coli and A. niger using the agar diffusion and challenge tests. The chemical stability was evaluated by HPLC in the reverse phase mode. A significant preservative instability was observed.

Qualitative and quantitative determination of Prevan in cosmetic emulsions by direct analysis via fast atom bombardment/collisional spectroscopy.

The qualitative and quantitative determination of the Na salt of dehydroacetic acid, Prevan, a widely employed antimould agent in cosmetic emulsions, has been obtained by the direct analysis of the emulsion itself by fast atom bombardment and collisional spectroscopy.

High-performance liquid chromatographic determination of free formaldehyde in cosmetics.

An improved, sensitive method for the determination of formaldehyde in cosmetics and other commercial products is reported. The procedure is based on dilution of the sample with tetrahydrofuran-water (9:1), followed by precolumn derivatization with 2,4-dinitrophenylhydrazine and direct reversed-phase high-performance liquid chromatography. The formaldehyde derivative is stabilized in the reaction medium by addition of phosphate buffer and neutralization and detected in less than 10 min by the standard additions methods. The method also appears to be suitable for the direct evaluation of the formaldehyde donors used in cosmetics as preservatives.

Dehydroacetic acid sodium salt stability in cosmetic preservative mixtures.

Synopsis Dehydroacetic acid sodium salt Prevan (DHANa) stability in presence of other cosmetic preservatives as Bronopol, Germall 115 and Kathon CG was investigated through a HPLC method that permits simultaneous determination of binary and ternary mixtures of the above preservatives. A new molecule coresponding to 3,7-dimethyl-1H, 9H, 10H, dipyrano (4,3-b: 3',4'-e) pyran-1, 9-dione has been discovered to be spontaneously formed between DHA and free or released formaldehyde. Its structure has been established by means of elemental analysis, NMR and mass spectrometry aswell as its chromatographic and antimicrobial behaviour. The magnesium salt present as stabilizer in the Kathon CG solution can also cause the formation of insoluble magnesium salt from DHANa. The ascertained chemical interaction among these preservatives is therefore discussed as a function of their cosmetic application.

Chemical stability and microbiological reply of preservative systems in cosmetics: a direct correlation.

Synopsis The results of a chemical/microbiological comparative study on different preservative mixtures are reported. The aim of the investigation was to ascertain whether there was a correlation between chemical stability and microbiological activity. The studies were carried out directly in cosmetic emulsions preserved with different mixtures of Prevan, Bronopol, Germall 115 and Kathon CG. The degree of microbiological activity was tested with respect to E. coli, Ps. aeruginosa, Asp. niger, S. aureus using the agar diffusion test, over a period of 400 days. The chemical behaviour of the different mixtures was evaluated by HPLC in reverse phase mode. The emulsion samples were directly injected after dilution with a THF/H(2)O) (9/1) solvent mixture.