Essential oils have many safe and effective uses, but did you know that some have been shown to disrupt sex hormones?
Lavender and tea tree essential oils have been used for centuries for many uses. Lavender has relaxing properties.  Tea tree oil is highly antifungal and antibacterial. [2,3] However, based on recent scientific research, for men and boys, these oils need to be used sparingly when applied topically. They have been found to disrupt the male hormone testosterone, stimulate estrogen receptors, and can cause male breast growth, also called gynecomastia. 
This effect was discovered in a clinical study of three prepubertal boys who used topically applied lotions with tea tree and/or lavender oils and presented with gynecomastia after use and then resolved when the application of the lotion was ceased.
Later this effect was confirmed in in-vitro (in a petri dish) studies showing that indeed these oils disrupt hormonal signaling. These studies found that both lavender and tea tree oils block testosterone signaling to androgen receptors and trigger estrogen receptors. This promotes estrogen activity and prevents the activity of testosterone hormones.
Men, boys, and prepubertal girls should not use topical lavender or tea tree oil or skincare products containing lavender or tea tree oil regularly, especially around the chest area although diffusing the oils may be safe.
- de Sousa DP, Soares Hocayen P de A, Andrade LN, Andreatini R. A Systematic Review of the Anxiolytic-Like Effects of Essential Oils in Animal Models. Molecules. 2015;20(10):18620-18660. doi:10.3390/molecules201018620
- Oliva A, Costantini S, De Angelis M, et al. High Potency of Melaleuca alternifolia Essential Oil against Multi-Drug Resistant Gram-Negative Bacteria and Methicillin-Resistant Staphylococcus aureus. Mol J Synth Chem Nat Prod Chem. 2018;23(10):2584. doi:10.3390/molecules23102584
- Mondello F, De Bernardis F, Girolamo A, Cassone A, Salvatore G. In vivo activity of terpinen-4-ol, the main bioactive component of Melaleuca alternifolia Cheel (tea tree) oil against azole-susceptible and -resistant human pathogenic Candida species. BMC Infect Dis. 2006;6:158. doi:10.1186/1471-2334-6-158
- Henley DV, Korach KS. Physiological effects and mechanisms of action of endocrine disrupting chemicals that alter estrogen signaling. Horm Athens Greece. 2010;9(3):191-205. Accessed December 29, 2021. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4782146/