The mechanism by which key components of CPEOs, such as D-limonene, α-pinene, linalool, and β-myrcene, upregulate BAX in cancer cells to induce apoptosis has been confirmed in T-cell lymphoma cells, gastric adenocarcinoma cells (AGS), human hepatoma cells (HepG2), human breast cancer cells (MCF-7), and human oral cancer cells (OECM1) [75,76,77]. The gene discussed is BAX; the disease is hepatocellular carcinoma.