Farnesol (trans, trans-3,7,11-trimethyl-2,6,10-dodecatriene-1-ol) is an essential oil component that can be found in a variety of plants. In this study, in vitro effects of farnesol on human lung cancer A549 cell line, colon adenocarcinoma (Caco-2) cell line and healthy human lung epithelial BEAS-2B cell lines, WST-1 cytotoxicity test, dual staining of cell survival (DAPI-PI) analysis, micronucleus test, and transmission electron microscopy (TEM). Farnesol acted in a concentration-dependent manner at the dose ranges studied for cancer cell lines, and while at certain doses it reduced proliferation, interestingly at higher concentrations it induced growth more than the control. In the healthy BEAS-2B cell line, it was tested over a wide range of doses and at all studied concentrations, it did not suppress cellular growth, but rather increased. This seems promising in that farnesol harms cancer cell lines but does not cause significant damage to healthy cells. Obtained TEM data after treatment with farnesol at IC50 dose showed both autophagic and apoptotic findings in cancer cell lines compared to control, and normal findings exhibited in BEAS-2B cell line, cell survival, and micronucleus analyzes showed the presence of apoptotic findings and chromosomal damage as a result of farnesol application in cancer cell lines. Research Highlights• Farnesol has dose-dependent effects on human lung cancer and colon adenocarcinoma cell lines, with no significant damaging effects on healthy human lung epithelial cell lines.• TEM, cell survival, and micronucleus findings support the findings of autophagic, apoptotic, and chromosomal damage on cancer cell lines.