EFFICACY AND TOLERANCE OF EXFOLIATING AGENTS 255 pigmentation disappearance and to investigate the effi cacy of exfoliating agents in induc- ing skin regeneration. Through the use of this method, we observed the different capaci- ties of the tested acids to increase the rate of skin regeneration, with a signifi cant reduction in the time required to obtain skin renewal. Topically applied at a 10% w/w concentra- tion, grape acids showed an exfoliating effect signifi cantly different from that of mandelic acid but were less active in comparison with glycolic acid. It is believed that at this concentration AHAs decrease corneocyte cohesion and enhance skin desquamation by Figure 3. Trends of the erythema index (Δ.E.I.) vs time (hours) for GLY (glycolic acid), MAN (mandelic acid), and GA (grape acids) formulations at three different concentration, (a) 10%, (b) 30%, and (c) 50% w/w, recorded after topical application over the monitoring period of 50 hours.

JOURNAL OF COSMETIC SCIENCE 256 acidifi cation of polar domains present within the hydrophilic lipid bilayers or by activation of acid protease crucial for desmosomal degradation (6). Furthermore, it has been reported that AHAs with a small molecular size are more active because they penetrate the skin more deeply (11). Glycolic acid is the simplest AHA, and it has the smallest molecular weight and size, followed by lactic, malic, tartaric, and citric acids, etc. This may explain the fact that glycolic acids tend to better penetrate the skin and accelerate skin regenera- tion. Mandelic acid and the organic acids contained in grape juice (tartaric acid, malic acid, citric acid, lactic acid, gluconic acid, and shikimic acid) have a greater molecular size and have more diffi culty in penetrating the skin. On the other hand, since the chemical peeling produces an insult to the skin, several side effects, such as erythema and redness, develop after treatment with exfoliating agents (3,9). Moreover, recent studies report that short-term dermal exposure with low concen- trations of exfoliating agents results in increased photosensitivity to UV light, measured as increased erythema and tanning (13,24). Skin tolerance to the exfoliating treatment is usually assessed by a visual and subjective record system. However, when objective and quantitative data are required, an instru- mental and non-invasive method is preferred for more accurate evaluations of the adverse skin effects. To this end, the skin tolerance and the photosensitizing effects of exfoliating acids were investigated by refl ectance spectrophotometric in vivo evaluation of skin ery- thema induced by topical application and after UV-light exposure. Since erythema is due to an increment in blood count in the subpapillary plexus of the skin and none of the main skin chromopheres (hemoglobin and melanin) absorb in narrow bands, the ery- thema index is not exclusively a linear function of hemoglobin content, but is affected by skin melanin content (25). On the basis of these assumptions, the skin refl ectance spectra, obtained by recording information on the optical spectrum of visible light ranging from 400 nm to 700 nm, is regarded as an accurate and reliable evaluation of the skin hemo- globin amount. Thereafter, the skin refl ectance spectral values permit calculation of the erythema index by subtracting the main melanin absorption peaks (510 and 610 nm) from the hemoglobin absorption peaks at wavelengths of 540 nm, 560 nm, and 580 nm Figure 4. Increase in skin sensitivity to UVB irradiation expressed by photosensitivity percentage after short-time treatment (four weeks) with GLY (glycolic acid), MAN (mandelic acid), and GA (grape acids) formulations containing 10% of acids vs control (no topical treatment). The photosensitivity % values were calculated from the erythema index obtained 24 hours after UVB exposure for each subject participating in the study.