The Toxic Effects of Tea Tree Oil for Treatment of Demodex Mites

Research published in Cornea indicates that tea tree oil component, terpinen-4-ol (T4O), may display toxic effects on human meibomian gland epithelial cells, raising concerns about its safety as a treatment for eye conditions related to Demodex mites. 

The study centered on the hypothesis that T4O, which is effective in killing Demodex mites, may also cause damage to human meibomian gland epithelial cells (HMGECs). To test this, they studied the effects of T4O on the morphology, survival, signaling ability, and differentiation of immortalized HMGECs.  

The identity of IHMGECs was confirmed using short tandem repeat (STR) profiling. DNA was extracted from cells at different passages and sent for STR profiling at the University of Arizona Genetics Core. The results were compared with the DSMZ database, and a match was considered if there was at least 80% identity at 8 core loci.  

IHMGECs were cultured in keratinocyte serum-free medium (KSFM), supplemented with epidermal growth factor (EGF) and bovine pituitary extract (BPE). After reaching confluence, cells were seeded in 12-well culture dishes for the experiments. To explore the short-term effects of T4O, IHMGECs were treated with different concentrations of T4O or vehicle for up to 90 minutes. To assess the long-term influence of T4O, IHMGECs were exposed to various doses of T4O or the vehicle for 5 days. Cellular morphology was observed using a phase-contrast microscope. 

“Experimental procedures included analyses of cell appearance, survival, P-Akt signaling, lysosome accumulation, and neutral lipid content,” said researchers.  

Researchers found that T4O has a negative impact on the survival of IHMGECs, with the extent of the effect depending on the dose and duration of exposure. After just 15 minutes of exposure to 1% T4O, significant changes were observed in the cells including rounding, atrophy, and poor adherence.  

Furthermore, almost all cells treated with 1% T4O died within 90 minutes. Lowering the T4O concentration to 0.1% also resulted in a noticeable decrease in both P-Akt signaling and IHMGEC survival. Interestingly, reducing the T4O amount to 0.01% only slightly reduced the number of IHMGECs after 5 days of culture, but did not affect their ability to differentiate. 

“T4O, even at levels 10- to 100-fold lower than demodicidal concentrations, is toxic to HMGECs in vitro,” said researchers.  

Reference 

Chen D, Wang J, Sullivan D A, et al. Effects of terpinen-4-ol on meibomian gland epithelial cells in vitro. Cornea. 2020;39(12): 1541–1546. doi:10.1097/ICO.0000000000002506