Anti-Demodex activity of castor oil confirmed in an ex vivo study.

Purpose: Periocular castor oil application shows possible benefits in managing Demodex blepharitis based on visibly reduced cylindrical dandruff at the base of the eyelashes, but the antidemodectic mechanism remains unclear. This research sought to establish Demodex mite susceptibility to castor oil directly in a controlled, ex vivo study.

Methods: Motile Demodex mites from epilated eyelashes with visible cylindrical dandruff were exposed to 5 µL aliquots of one of four castor oil or tea tree oil-based preparations, or remained unexposed (negative control). Adult Demodex mite motility was confirmed by high magnification microscopy every 5 min for up to 480 min post-exposure and survival time recorded when movement ceased. Tested oils were 100% cold-pressed castor oil, a proprietary castor oil preparation containing identical castor oil combined with manuka and kanuka oils, and 100% and 50% tea tree oil as positive controls.

Results: Survival time in the negative control group exceeded 480 min. All tested oils exhibited shortened mite survival time relative to the negative control (p < 0.05 in all cases). Survival times for 59 mites from 12 participants were plotted for the 5 experimental groups. Undiluted and proprietary castor oil preparations exhibited median (interquartile range; IQR) survival times of 235 (200-285) and 325 (240-405) minutes, respectively, with no significant difference between groups (p > 0.05). A single mite from each castor oil group survived beyond 480 min. Positive controls exhibited median (IQR) survival times of 5 (5-10) mins for 100% tea tree oil and 20 (15-25) mins, for 50% tea tree oil.

Conclusions: Castor oil alone, or in proprietary form supplemented with manuka and kanuka oils, reduced Demodex survival over an 8-hour period. Outcomes suggest extended duration exposure to castor oil, such as in overnight application, has demodecidal activity that could contribute to Demodex blepharitis management.