A word of warning:
Do NOT use Tea Tree Oil (Melaleuca oil) on hot spots. Tea Tree Oil can cause neurological damage and even death when absorbed directly into the blood stream.
At one point in time, it was commonly recommended for hot spots, but I learned a hard lesson that just because something is 'all natural' doesn't mean it's at all safe.
I had a dog with a hot spot, and applied tea tree oil to the area. The next day, Vinne was paralyzed from the neck down. The emergency vet's initial diagnosis was degenerative disk disease, which is a death sentence for Frenchies. Luckily I insisted on a second opinion, rather than following the vet's advice to put him down immediately. The specialist vet inquired about his hot spot, and told me about the neurological side effects of tea tree oil on dogs, cats and small children. Thankfully, Vin recovered with no side effects.
From the Animal Poison Control Center website:
"Clinical effects that may occur following dermal exposure to significant amounts of tea tree oil include loss of coordination, muscle weakness, depression, and possibly even a severe drop in body temperature, collapse and liver damage. If the oil is ingested, potential effects include vomiting, diarrhea and, in some cases, seizures. If inhalation of the oil occurs, aspiration pneumonia is possible. "
Details on neurological side effects of Melaleuca oil:
EC: Melagel is made from Tea Tree Oil...