476 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS many reflectance meters are immobile and cumbersome to use for measurements on subjects' forearms or backs. Recently Diffey and coworkers (4,5) quantified UV-light induced erythema using a small reflectance meter that records an erythema index. How- ever, this meter is a custom built apparatus. This paper describes the use of the Minolta Chroma Meter, a commercially available reflectance meter, to rapidly and accurately measure erythema caused by soap and detergent bars. The Chroma Meter is small, portable, and commercially available (cost $2,500). It contains a flexible probe that enables the subject to remain stationary while multiple sites are measured. We herein validate the use of this instrument for monitoring er- ythema levels in a soap chamber patch test situation by comparing instrumental readings with visual assessments. METHODS The relative irritancy of six cleaning bar products, four bar soaps (samples A, C, E, and F) and two detergent bars (samples B and D), was determined in a modified soap chamber test (6). Five percent solutions (w/w) of each were prepared in tap water (with gentle warming) and each sample was applied to a separate site on the volar forearm in a Duhring Chamber. Three sites on each of two forearms were treated for a given subject and 21 subjects participated (each signed an informed consent form). The study was run at KGL, Inc. (Philadelphia, PA) and was medically monitored at this facility. The chambers were removed after 24 hours, and the forearms were rinsed with warm tap water. After 3 hours, visual erythema scores were obtained by a trained evaluator, and instrumental assessments (Minolta Chroma Meter and evaporimeter) were obtained by a technician. The subjects were equilibrated for 1 hour at 68øF, 40-50% RH, prior to taking evaporimetry readings. The study was done double blind. The irritation caused by the six different treatments with soap and detergent bar solu- tions applied to human volar forearms was assessed by three measures: (i) visual scoring of erythema produced by the different samples using an arbitrary scale (6), (ii) Minolta Chroma Meter measurements of redness, and (iii) transepidermal water loss (Evapo- rimeter, Servo Med, Inc., Montpellier, VT ref. 7). The six sites were also assessed by the three methods prior to treatment (control measurements). The Minolta Chroma Meter model CR-100 (Registered Trademark, The Minolta Com- pany, Minolta Corp. Ramsey, NJ) was used in this study (Figure 1). This instrument has a flexible, hand-held probe which can be moved from site to site on the subject's arm with ease. The aperture of the probe (8 mm diameter) is rested lightly on the skin. All readings were taken by the same technician so that approximately the same amount of pressure was applied to each site. Readings can be taken in 15 seconds or less. Blanching does not affect our results because the pressure of the probe on the skin is small and is the same for all sites. That the Chroma Meter readings closely correlate with visual scores (where no pressure is exerted on the test sites) supports this conclu- sion. The Chroma Meter is small (1-2 lbs) and also has the advantage of being battery powered if desired both facilitate easy transport of the equipment. The Minolta Chroma (Reflectance) Meter reads color in a three-dimensional format where the color system is that recommended by CIE, and the coordinates are L ½, a ½ and b • (1). The L • signifies levels of brightness between black and white. Coordinate "a •" signifies the balance between red and green with 100 being red only and - 100 being

ERYTHEMA QUANTITATION BY SKIN REFLECTANCE 477 i Figure 1. Photograph of the Minolta Chroma Meter (compliments of Minolta Corporation, Ramsey, NJ). Note the small size (8" by 3"by 2") and the convenient hand-held flexible probe. green. The "b*" coordinate signifies relative amounts of yellow and blue. Estimates of changes in redness intensity were made from the "a*" scale, but values for the other coordinates are available from the instrument. Table I Comparison of Instrumental and Visual Assessments of Skin Condition *Treatment Erythema Visual Assessment Minolta-Reflectance ( 4_-_ S.D.) Mean Rank _+ S.D. Before After Transepidermal Water Loss Evaporimetry (g/m2hr _+ S.D.) Before After A 4.2 + 1.3 7.5 -+ 1.5 9.8 + 1.8 5.1 + 3.0 11.4 + 2.6 B 2.5 + 1.2 7.8 + 2.5 8.9 -4-_ 1.7 4.8 + 1.2 9.3 -+ 2.3 C 3.7 -+ 1.1 7.0 + 1.4 9.9 -+ 2.1 4.5 + 1.2 13.5 + 2.7 D 2.1 _+ 0.9 7.1 _+ 1.7 8.8 + 1.9 4.4 + 1.0 8.9 + 2.1 E 4.8 + 1.2 7.5 + 1.8 10.1 + 1.9 4.8 _+ 1.7 13.2 -+ 3.4 F 3.8 + 1.2 7.4 + 1.8 9.5 --+ 1.9 4.8 + 1.5 11.2 + 2.8 * Samples tested were 5 % solutions of various soap and detergent bars. For each assessment, values shown are means of 21 individual patch sites for each sample + standard deviation (S. D.). The six visual scores for each subject were ranked as described in the text. For each column of after-treatment values, means for treatments B and D were not statistically different from each other but were significantly different from the other four treatment means. Treatments A, C, E, and F were not significantly different from each other. Statistical analysis was as described in the text.