According to MedlinePlus, tea tree oil is safe to use topically throughout pregnancy. While tea tree oil should never be taken internally because it is toxic, it can be directly applied to the skin during pregnancy or added to a carrier oil or some other dilution. Derived from the leaves of the tea tree, tea tree oil is used as an antiseptic and antifungal alternative treatment.
Tea tree oil is most commonly used to treat acne, fungal infections of the nails, ringworm and athlete's foot, according to MedlinePlus. It is also effective when applied to cuts and abrasions resulting from insect bites and stings, boils and injuries. Tea tree oil can also be added to bath water to aid in healing and to provide relief from bronchial congestion and colds.
According to the Mayo Clinic, while there is little scientific research on the topic, tea tree oil should be used cautiously during pregnancy, as its use can cause decreased contraction strength. However, it is considered safe for use on the skin.
The Mayo Clinic reports that some people experience an allergic skin reaction to the use of tea tree oil that manifests as anything from contact dermatitis to severe blistering. If this occurs, use of tea tree oil should be discontinued. For the best results and to avoid any potential side effects, only the recommended dosage of tea tree oil should be used during pregnancy.