Without reading the article (in a rush again) I wouldn't dare comment on the contents of the oils Genie is referring to but there are still a couple of clarifications useful to the discussion.
"I'm not surprised that Melaleuca Oil didn't work on flea bites or that it might have even made the irritation worse. I don't think the oil is touted as an "anti-itch" solution, and since it's a solvent, it probably would carry the itch-causing agent further into the skin."
I wasn't dealing with an itch agent but an infection; when fleas bite they open the skin and various bacteria can get into the subcutaneous tissues and bloodstream. Because I was in the wet tropics during the Wet I wasn't interested in prolonging the vulnerability to nasties that can prove difficult to eradicate. I was testing the oil as a topical antiseptic/antibiotic on infected but superficial lesions; the oil just increased the irritation and had no discernable topical antiseptic/antibiotic effect on them. The oral antibiotic worked.
And to assure readers that I take a lot of convincing before I "believe" claims about medications, I was once put on a charge (when in the weekend warriors) for refusing an order to take an aspirin. We'd been ambushing some gumtree or other on a blistering January afternoon and the medico (who had his subaltern's pips purely because he was a 4th year student in medicine) ordered our platoon to take water (which I did) and an aspirin each, which I refused on the basis of understanding that aspirin was an analgaesic and I routinely avoided them. I didn't know (and he, silly bugger, hadn't the knowledge or the wit to tell me) that aspirin is also an antipyretic useable as a prevention as well as a treatment of heat stress. Silly bugger me.
Back to the thread topic, I wasn't surprised about claims that the essential oils collection had 'gone off' either, given the length of storage time, but I doubt anyone then or now has any "real" info on such behaviour of substances that have been used as folk remedies for as long as there's been folk. Hooray for "evidence based assessment" in medicine.