21 CHARACTERIZATION AND ACTIVITY OF ESSENTIAL OILS and S epidermidis, respectively. In another study, the MIC and MBC values of lavender were 0.125, cinnamon 0.016, and lemon 0.250% (v/v) against P acnes (42). FRACTIONAL INHIBITORY CONCENTRATION INDEX OF THE BINARY COMBINATION OF ESSENTIAL OILS Possible synergistic effects of eight antibacterial effective EOs in dual combinations were investigated using the checkerboard method. FICI values were calculated and shown in Tables IV and V. Cinnamon/lavender and cinnamon/sandalwood EOs demonstrated the best activity with a synergistic effect (FICI ≤ 0.5) against both strains. In addition, cinnamon EO combined with lemon (FICI: 0.25) and eucalyptus (FICI: 0.27) eucalyptus EO combined with lavender (FICI: 0.50) and tea tree (FICI: 0.38) EOs displayed a synergistic action oregano/sandalwood (FICI: 1.00), cinnamon/tea tree (FICI: 0.63), and sandalwood/ lemon (FICI: 0.75) exhibited additive effect against S epidermidis. For C acnes, a synergistic inhibition effect and an additive effect were observed in the laurel/lavender (FICI: 0.047) and cinnamon/laurel (FICI: 0.563) EO mixtures. According to previous studies, tea tree in dual combination with lemon (FICI: 1.00), lavender (FICI: 1.00), eucalyptus (FICI: 0.75), and sandalwood (FICI: 0.98) and lemon with lavender (FICI: 1.00) and eucalyptus (FICI: 0.83) showed an additive effect against C acnes. On the other hand, tea tree in combination with lemon (FICI: 0.66), lavender (FICI: 0.56), and eucalyptus (FICI: 0.19) showed a synergistic Table II Inhibition Zone Diameters (mm) of EOs EOs S epidermidis ATCC 12228 p value C acnes ATCC 6919 p value Or 74.00 ± 5.888 p 0.0.1 37.50 ± 0.577 p 0.0.1 Lau 11.75 ± 0.957 p: 1.00 20.75 ± 0.957 p 0.0.1 Gi – – – – Ci 53.75 ± 1.708 p 0.0.1 40.00 ± 1.633 p 0.0.1 O – – – – La 28.50 ± 2.646 p 0.0.1 28.25 ± 1.258 p 0.0.1 Ch – – 8.75 ± 0.50 p: 0.478 (Ery) p: 0.540 (Clin) Sa 13.00 ± 0.817 p: 0.996 (Ery) p: 0.974 (Clin) 15.50 ± 0.577 p 0.0.1 Te 23.50 ± 3.109 p 0.0.1 22.00 ± 0.817 p 0.0.1 Le 19.75 ± 0.957 p 0.0.5 – – Eu 18.00 ± 1.414 p: 0.22 (Ery) p: 0.11 (Clin) 20.00 ± 0.817 p 0.0.1 Ro – – 8.75 ± 0.957 p: 0.629 (Ery) p: 0.677 (Clin) Ga – – 8.25 ± 0.50 p: 0.478 (Ery) p: 0.540 (Clin) Co – – – Cl – – 8.75 ± 0.50 p: 0.478 (Ery) p: 0.540 (Clin) Sag – – 9.00 ± 0.817 p: 0.577 (Ery) p: 0.629 (Clin) Ery 11.50 ± 0.577 11.00 ± 0.817 11.00 ± 0.817 11.25 ± 0.957 Clin Tween 80 – – Or: oregano Lau: laurel Gi: ginger Ci: cinnamon O: orange La: lavender Ch: chamomile Sa: sandalwood Te: tea tree Le: lemon Eu: eucalyptus Ro: rosemary Ga: garlic Co: coconut Cl: clove Sag: sage Ery: erythromycin and Clin: clindamycin as positive controls negative control: Tween 80 -:no inhibition results are mean—± standard deviation (SD).

Table III MIC and MBC Concentration Values of EOs (v/v %)on Standard Strains Causing Acne Bacteria Activity Or La Le Sa Ci Te Eu Lau S epidermidis ATCC 12228 MIC MBC 0.03125 0.03125 1.00 2.00 16.00 32.00 32.00 32.00 0.25 0.50 0.50 1.00 4.00 8.00 – C acnes ATCC 6919 MIC MBC 0.0625 0.0625 16.00 32.00 – 16.00 16.00 2.00 4.00 1.00 2.00 32.00 64.00 4.00 4.00 Or: oregano La: lavender Le: lemon Sa: sandalwood Ci: cinnamon Te: tea tree Eu: eucalyptus Lau: laurel. 22 JOURNAL OF COSMETIC SCIENCE