Tea tree oil (TTO), a substance also known as melaleuca oil, comes from the Australian tea tree and has been used by humans to treat acne, athlete’s foot, lice, nail fungus and insect bites. More likely than not, you can find it in several over-the-counter skin care products and essential oils at your local drug store and Amazon. TTO has been used as a traditional medicine by Australian Aborigines for centuries, and the substance has a variety of natural ingredients that have been shown to kill certain bacteria, viruses and fungi.