I have no problem with people considering "alternative" therapies for the treatment of infections. I perform research on non-antibiotic alternatives and hope that results pan out in the field. I have problems, however, with people that use unproven alternative therapies in lieu of proven conventional treatment or stray from the "do no harm" philosophy.
I read an article on aromatherapy in pets that highlighted my concern. Someone can make Fluffy or Fido smell whatever they want (although my dog Meg’s concept of what smells nice certainly differs from mine – she’d rather roll around on a decomposing carcass than a lavender plant). I don’t think it’s going to help, but it shouldn’t hurt. This article went beyond that, though, talking about application of substances to treat infections. Putting tea tree oil into a dog’s ear isn’t aromatherapy, it’s topical therapy.
Is it an issue of semantics? No.
Essential oils like tea tree oil have some powerful properties. Just because it’s "natural" doesn’t mean it’s safe. We know that tea tree oil has antibacterial properties. However, we also know it can be toxic. There are reports of serious adverse effects in people from tea tree oil ingestion and I know of severe reactions in dogs (including 1 death) thought to be due to excessive tea tree oil application. Adverse effects can result from the dog ingesting the oil by licking it off its coat or from direct effects on the skin.
A research study presented by Dr. Becky Valentine at the 2011 North American Veterinary Dermatology Forum highlighted this concern. Her research showed that while tea tree oil was able to kill methicillin-resistant Staphylococcus pseudintermedius (MRSP), a leading cause of canine ear and skin infections, it was also quite toxic to canine skin cells. So, the cost-benefit of tea tree oil is unclear since it certainly has some toxic properties, particularly when compared to other topical therapies such as chlorhexidine, that are essentially non-toxic.
Additionally, in a good demonstration of "all pain, no gain," Dr. Valentine’s research showed that grapefruit seed extract, another compound available over the counter, had no effect on MRSP but had significant toxic effects on canine skin cells.
What does this mean? It means that essential oils and any other alternative therapies need to be studied, just like any other treatment. We need safety studies to know they won’t cause problems, dosage studies to know how to use them and efficacy studies to know if they work. Natural products can be quite powerful and potentially useful, but they need proper testing.