## Materials and Methods
### Clinical Evaluation
#### 2.6.6 Efficacy Evaluation  
With the same group of volunteers, anti-sebum efficacy evaluation tests were conducted with the highest concentration emblica toner that was stable and non-irritating. After resting for 30 min to acclimatize to ambient conditions, the facial skin sebum levels of volunteers were measured at each position, designated as specified in Figure 1, at 23-25 \({}^{\circ}\)C and 40-60% relative humidity. Herein, the facial skin sebum level, which was measured 1 h before washing, was called the \"Casual Level\". The facial skin of each volunteer was cleaned with the same mild facial cleanser except the area covering the position F\({}_{0}\), and, after that (0 h), its sebum level was measured. The volunteers were randomized to apply 2 cm\({}^{3}\) of emblica toner on the left or right side of each of their faces by block randomization (from randomization.com) and to apply 2 cm\({}^{3}\) of toner base on the other side using cotton balls, except the area covering the position F\({}_{\text{C}}\), as specified in Figure 1. The sebum level of each position was measured again after 1, 2, 3, and 4 h, as shown in Figure 2, and then the sebum recovery and the anti-sebum efficacy was calculated as follows:  
The sebum recovery of facial skin for treatment X at time t (SR\({}_{\text{X,t}}\)) was calculated by comparing the facial sebum level with the casual level (baseline) of each position in percentage value:  
\[\text{SR}_{\text{X, t}}=\frac{\text{S}_{\text{X, t}}}{\text{S}_{\text{X,-1}}} \times 100\%. \tag{1}\]  
Figure 1: Positions on facial skin for specified methods of treatment. F\({}_{0}\) = unwashed (non-treatment) on forehead; F\({}_{\text{C}}\) = washed only (control treatment) on forehead; F\({}_{\text{B}}\) = washed + toner base on forehead; F\({}_{\text{E}}\) = washed + emblica toner on forehead; C\({}_{\text{B}}\) = washed + toner base on cheek; C\({}_{\text{E}}\) = washed + emblica toner on cheek.  
Figure 2: Steps in the experiment.  
where:  
SR\({}_{\chi,t}\) = Sebum Recovery after washing and applying Toner X at time t;  
S\({}_{\chi,-1}\) = Sebum casual level at 1 h before treatment X was applied;  
S\({}_{\chi,t}\) = Sebum level for treatment X at time t.  
The anti-sebum efficacy of toner X at time t (as\({}_{\chi,t}\)) was calculated by comparing the sebum recovery of toner X with the sebum recovery of washed only (control treatment) position at time t in percentage value:  
\[\text{as}_{\chi,t}\ =\frac{\text{SR}_{C,t}\ -\ \text{SR}_{\chi,t}}{\text{SR}_{C,t}} \times 100\%. \tag{2}\]  
where:  
as\({}_{\chi,t}\) = Anti-Sebum Efficacy of toner X at time t (1, 2, 3, 4 h);  
SR\({}_{C,t}\) = Sebum Recovery after being washed only (control treatment) at time t (1, 2, 3, 4 h);  
SR\({}_{\chi,t}\) = Sebum Recovery after being washed and Toner X applied at time t (1, 2, 3, 4 h).  
Since the sebum recovery changed over time, as shown in equation No. 2, anti-sebum efficacy of toner X on the facial skin over period t (AS\({}_{\chi,t}\)) can be calculated by comparing the area under the curve (AUC) of the sebum recovery of toner X with that of the washed-only (control treatment) position of each period in percentage value:  
\[\text{AS}_{\chi,t}\text{=}\frac{\text{AUC}(\text{SR}_{C,t})_{t-1}^{t}\ -\ \text{AUC}(\text{SR}_{\chi,t})_{t-1}^{t}}{\text{AUC}(\text{SR}_{C,t})_{t-1}^{t }}\times 100\% \tag{3}\]  
where:  
AS\({}_{\chi,t}\) = Anti-Sebum Efficacy of toner X over period t (1, 2, 3, 4 h);  
AUC(SR\({}_{C,t})_{t-1}^{t}\) = AUC of Sebum Recovery after being washed only (control treatment) over period t - 1 to t (1, 2, 3, 4 h);  
AUC(SR\({}_{\chi,t})_{t-1}^{t}\) = AUC of Sebum Recovery after being washed and Toner X applied over period t - 1 to t (1, 2, 3, 4 h).