Side Effects and Warnings

Tea tree oil taken by mouth is associated with potentially severe reactions, even when used in small quantities. Several reports describe people using tea tree oil by mouth who developed severe rash, reduced immune system function, abdominal pain, diarrhea, lethargy, drowsiness, inflammation of the corners of the mouth, slow or uneven walking, confusion, or coma. There have also been reports of nausea, unpleasant taste, burning sensation, and bad breath associated with tea tree oil use. Many tea tree preparations contain large volumes of alcohol.

When used on the skin, tea tree oil may cause allergic rash, redness, blistering, and itching. Use of tea tree oil inside of the mouth or eyes can cause irritation. One report describes a person with long-standing eczema (atopic dermatitis) who developed a severe flare after applying 100% tea tree oil mixed in honey to the skin. Animal research suggests that tea tree oil used on the skin in large quantities can cause serious reactions such as difficulty walking, weakness, muscle tremor, slowing of brain function, and poor coordination. When applied in the ears of animals, 100% tea tree oil has caused reduced hearing, although a 2% solution has not led to lasting changes in hearing. The effect of tea tree oil on hearing when used in the ears of humans is not known.