260 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS openings for the subsite measure at least 1• cm x 1• cm for ease in centering the 1 cm diameter beam of the solar simulator (see Light Source, below). Thus, no more than six subsites can readily be used with the "standard" model template. The range-finding technique permits the irradiation of seven sites, with a range through three expected SPF values. MATERIALS AND METHODS TEST MATERIALS Five sunscreen products, ranging in SPF values from 2 to 15, were tested together with 8% homosalate (HMS) (SPF = 4), which was used as the control. The sunscreen products were transferred to coded laboratory bottles and tested blind. 100/xl of each product was drawn up into a 100/xl syringe (Model MB, Drummond Scientific), and spread evenly with a finger cot in the 50 cm 2 template area, which was previously outlined on the subject's skin with gentian violet surgical marker. LIGHT SOURCE The Solar Ultraviolet Simulator Model 10S (Solar Light Company, Philadelphia, PA) (2) consisting of a 150 watt xenon arc lamp, all required optical elements, and a regulated power supply was used. SUBJECTS The subjects were five healthy volunteers of Skin Types I (always burn easily never tan) II (always burn easily tan minimally) and III (burn moderately tan gradually). All subjects gave informed consent and had no medical condition preventing their participation. All test products were used on all subjects. The placement of products was random on each subject, using a programmed-calculator-generated table of random numbers. Template anatomical placement sites were designated one through six from left to right, top to bottom, of the subject's back. RANGE-FINDING METHOD The Monograph (1) requirement of a 50 cm 2 test area is satisfied by using a 25 x 2 cm template. In a range-finding assay testing for an SPF -- 4, 6, or 8, irradiation times are calculated as follows: Let X = subject's unprotected MED. The seven subsites receive the following irradiation times: #1 = 3.0X #2 = 4.0X #3 = 5.0X //4 = 6.0X #5 = 7.5X if6 = 8.0X #7 = 10.OX. RATIONALE The second, fourth, and sixth subsites receive "expected" SPF values of 4, 6, and 8, respectively, i.e., subsite #2 is irradiated for 4.0X sec, subsite #4 is irradiated for 6.0X sec, and subsite #8 is irradiated for 8.0X sec. As per Monograph (1) requirement, subsite

SUN PROTECTION FACTOR 261 //1 receives 25% less irradiation than subsite//2, i.e., 3.0X sec. Subsite//3 receives 25% more irradiation than subsite//2, i.e., 5.0X sec. Subsite//5 receives 25% more than subsite if4, i.e., 7.5X sec. Subsite//7 receives 25% more irradiation than subsite//6, i.e., 10.OX sec. Note that the irradiation time at subsite//4 equals a 25% decrement from subsite//6. The only (minor) exception to the bracketing of each of the three expected SPF values occurs at subsite//3, which is 0. SX sec additional time rather than a full 25% decrement from the irradiation time at subsite//4. It is more important to give the subject the full 25% increment over 4.0X sec to see whether or not the product is in the SPF = 4 range, which encompasses 4.0 through 5.99. For a product to be tested for an SPF = 2, 4, or 6, all values are calculated one step down for an SPF = 6, 8, or 15, range-finding test, all values are calculated at one step up. In a range-finding test irradiated as outlined above, the product is an SPF = 4 if no MED is observed at subsite//1, but is present at subsite//2 or//3. If no MED of the protected skin is observable until subsite//4 or//5, the product is an SPF = 6. If the first observable MED occurs at subsite//6 or//7, the product is an SPF = 8. The range-finding method can be used on only the first five subjects if the data warrants, subsequent irradiation of the fifteen additional required subjects can be done in the time-saving customary manner, using a conventional 5 x 10 cm irradiation site. To blind the experimentation further, laboratory personnel were instructed to conduct: (A) an SPF = 2, 4, or 6 range-finding assay on all five subjects with the products known to be SPF = 2, and on three subjects with the product known to be SPF = 4 (B) an SPF = 4, 6, or 8 range-finding assay on two of the subjects with the product known to Table I SPF Values Achieved 8% HMS Product Code EI OE EN LE ON Control SPF value as marketed 2 4 6 8 15 4 Range-Finding Test(s)* used A = all A = 3, B = 2 B = 4, C = 1 B = 2, C = 3 C = all A = all Subj # 1 2.0 4.0 6.0 7.5 15.0 4.0 2 2.0 4.0 7.5 7.5 15.0 4.0 3 2.0 4.0 6.0 8.0 10.0 4.0 4 2.0 4.0 5.0 10.0 15.0 4.0 5 2.0 4.0 6.0 8.0 18.7 4.0 __ •*X = SPF 2.0 4.0 6.1 8.2 14.7 4.0 SD 0 0 0.8 0.93 2.77 0 SE 0 0 0.357 0.414 1.24 0 SEM% 0 0 5.86% 5.06% 8.43% 0 *Range- Finding Test Designation A=SPF=2,4or6 B =SPF=4,6or8 C =SPF=6,8or15 -- **X = SPF = Sun Protection Factor (Mean) SD = Standard Deviation SE = Standard Error SEM% = Standard Error of the mean (%)