Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.

Is tea tree oil toxic? “Anecdotal evidence…suggests that the topical use of the oil is relatively safe, and that adverse events are minor, self-limiting, and occasional. Published data [however, add some caveats: it can be] toxic if ingested…and can also cause skin irritation at higher concentrations.”

Now, normally, “[t]ea tree oil reduces…skin inflammation.” 27 volunteers had histamine injected in their skin—the equivalent of getting bitten by a fire ant. But the big red swollen marks “significantly decreased” after the application of tea tree oil. Here’s where the bump was at 20 minutes after injection. Apply a placebo oil, and it continues to get worse before finally beginning to calm down. But, if at 20 minutes, you apply half of a single drop of pure tea tree oil, it stops the inflammation in its tracks, and it immediately starts to get better.

Some people are sensitive to it, though, and it can instead trigger a rash. This is relatively rare, though, with only about 1% of older children or adults having such a reaction. None of the 40 younger children tested had a reaction, which is good, since it may be found in like 5% of diaper wipes and lotions.

“Most reactions [when they do occur] are caused by the application of pure oil.” So, there are recommendations to keep the concentration of tea tree oil products applied to the skin under 1%. Moreover, manufacturers may want to use antioxidants and dark bottles “to minimize exposure to light,” since aged, oxidized oils are more likely to induce allergic reactions. Hundreds of different components have been identified in tea tree oil, but the composition changes “when…exposed to air, light, humidity, and higher temperatures.” It can start turning “a green–brownish color, the viscosity changes, and the smell becomes turpentine-like.” All bad signs.

Even fresh tea tree oil shouldn’t be ingested, though. Two hours before arriving at the pediatric critical care unit, a four-year-old’s mother “had given him approximately 2 teaspoons of…tea tree oil.” Within 30 minutes, he had trouble walking, and shortly thereafter fell into a coma. They note the tea tree oil was in a bottle without a childproof cap, but it didn’t matter in this case, because the cap wasn’t mother-proof, either.

Similar cases are reported at even less than two teaspoons, though the reported adult poisoning cases have tended to involve larger doses. Thankfully, “[n]o human deaths caused by [tea tree oil] have been reported,” though note the qualifier “human.” It has been implicated in the deaths of pets when used inappropriately when trying to treat fleas or something. “Cats in particular are at risk because of their habit of licking their fur.”

In humans, though, it can apparently be used safely if you “avoid…ingestion, apply…only diluted oil topically, and only [use] oil that has been stored correctly.”

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