370 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS MATERIALS AND METHODS INSTRUMENTATION Chromameters measure surface color and surface darkness/lightness to a precise degree by illuminating the site with a pulse or flood of light of defined color/brightness from a xenon arc lamp. The reflected light divides three ways, passes through filters, and strikes silicon photocells. Upon striking the silicon photocells, light energy is con- verted into an electrical signal and sent to a microprocessor where it is converted into coordinates for the chosen color space. Data output is in the form of L*, a*, and b* values. L* corresponds to levels of darkness/lightness between black and white. Coordi- nate a* signifies the balance between red/green, and b* between yellow/blue. For skin measurements, the q- a* range is of particular interest in measurements of erythema. L* or reflectance values are useful in tanning studies. ERYTHEMA ASSESSMENT: ANTI-IRRITANCY STUDIES A number of experiments have been designed to study the anti-irritancy effect of skin treatment products. The volar forearm of healthy volunteers (age 23-35 yr) is a conve- nient site for such studies, although facial skin can be more sensitive. Studies were done with different types of irritants. The most commonly used irritant in our studies is Balsam of Peru in petrolatum. Balsam of Peru is a syrupy balsam from a tropical Amer- ican tree (Myroxylon perurae) growing chiefly in E1 Salvador. It contains fragrance oils and has been used in perfumery. However, a majority of the cosmetic-using population has been reported to react to it. The immediate reaction to this compound is in the form of urticaria, which is an irritancy reaction, not involving the systemic antigen-anti- body reactions observed in sensitization reactions (4). Format of the study. Two 3-cm-square areas were delineated on the forearms of 14 volun- teers. Baseline skin color measurements were noted on both sites as a* values of the chromameter. One site was treated with an anti-irritant. The material was allowed to absorb for 20 minutes, and then Balsam of Peru was applied on the treated as well as the adjacent untreated control site. Degree of redness (a* values) was recorded at its maximal point after 25-45 minutes. Anti-irritant effects were determined by comparing a* values of the treated site with control sites. Baseline redness values of the skin were subtracted from each measure- ment. In other studies, anti-irritant materials such as indomethacin or hydrocortisone were applied 15-20 minutes prior to the irritant. Baseline measurements of both treated and untreated sites were obtained prior to application of the stimulus or anti-irritant mate- rial. Visual scoring of erythema was determined by a panel of trained judges. Results were evaluated with a statistical package (Statgraphics) to assess significance. TANNING STUDIES Assessing tanning accelerators requires precise and objective quantification of skin dark-

ANTI-IRRITANTS AND TANNING ACCELERATORS 371 ening in response to UV irradiation. L* values are used for measurement of skin light- ness. For a complete picture of the tanning response, AE* can be calculated as follows: A E* = X/(A L*) 2 q- (A a*) 2 q- (A b*) 2 AE* then represents the linear combination of changes in both skin reflectance as well as color. In the following studies skin tanning was assessed visually as well as with L* values measured by the chromameter. The MED for each panelist was determined to obtain the optimum UV dose for the experiment. Tanning products were applied on the skin before or after exposure to the solar simulator, at the appropriate UV dose levels. Twenty-four-hour erythema was measured by a* values, and after 48-72 hours tanning was determined by the change in L* values as compared with the control site exposed to the same dose of UV irradiation but not treated with tanning accelerator. Visual evalua- tion of tanning was conducted by a panel of trained judges on a 1-4 standardized scale. The results were evaluated with a statistical package (Statgraphics) to assess signifi- cance. RESULTS ERYTHEMA ASSESSMENT Correlation of instrumental and visual assessment. In order to determine if the results ob- tained from the chromameter measurements were in agreement with those obtained from visual assessment, we determined the correlation coefficient for results obtained via both measuring techniques (Table I). After subtracting the baseline skin measurements, the product-treated site values were subtracted from the a* value of the untreated site to obtain Aa* value (Table II). Visual scoring of skin erythema, as grade 1 to 4, based on a standardized scale, was done by a panel of trained observers and compared with the Aa* values obtained with the chromameter (Figure 1). The visual grading of skin erythema is generally consid- ered the difference between baseline skin color and increase in redness as observed by the eye. We found a significant correlation (r = 0.6785, p 0.001) between values obtained on increase of redness and visual grading of skin erythema. Anti-irritancy studies. The efficacy of an anti-irritant challenged by either a chemical or physical stimulus was determined in terms of inhibition of erythema (a* value) and compared with the skin area treated with irritant alone. Figure 2 shows two sites treated with the chemical irritant Balsam of Peru. Site B is a control that was not Table I Correlation Between Visual Scoring and Chromameter Readings for the Measurement of Skin Erythema Chromameter Visual Correlation grading A a* grading coefficient r n = 14 3.29 1.! 0.6785 (p 0.00!)