[jbotz]

Pure essential peppermint oil definitely works as a rodent repellent, even in very small quantities, although the effect wears off pretty quickly (that's the thing about essential oils, the essence is volatile). Plan to reapply every 3-7 days. Btw. the reason it works that that for rodents the sense of smell is primary, and mint smell overpowers everything else, so in its presence they are effectively blind.

[kragen]

Be careful with essential oils. In most cases the lethal dose for an adult human is about 5 grams.

[throwup238]

Do you drink your essential oils? Unless they’re laced with DMSO, I don’t see how five grams of the active ingredient could be absorbed.

[kragen]

Drinking them is usually how fatal doses are reached, yes. There isn't much risk topically, as you say, or by inhalation. I have read in the literature of one fatality from topical oil of wintergreen, I believe a teenaged marathon runner who was treating her muscle pain. I don't know if her preparation (an FDA-approved over-the-counter patch from a mainstream pharmaceutical company, if I recall) used DMSO or similar excipients. But such topical fatalities are very unusual.

But we are specifically discussing ingestion of non-recommended substances here.

To correct a minor misconception that could arise from your comment: essential oils do not contain active ingredients. They are, generally speaking, the active ingredient. Some, like oil of wintergreen, are an almost pure compound, while others, like oil of peppermint, are mixtures, but generally they do not contain inert or nontoxic components.

One specific way that a fatal dose could be ingested is if the person ingesting it had previously obtained adulterated essential oils from an irresponsible drug dealer, containing an active ingredient but consisting mostly of something like canola oil, and then switched to a pure essential oil without realizing it.

[throwup238]

I don’t think people are ingesting peppermint oil to ward off rats in a plow truck.

It really doesn’t matter how you classify the active ingredient (and there is absolutely an active ingredient). It’s not getting absorbed in five gram quantities unless you snort it, drink it, or apply a stupid homeopathic topical with DMSO that penetrates the skin.

Edit: you’ve edited your post several times since I’ve made mine and I’m just not going to bother. There a dozen everpresent household chemicals that are deadlier than essential oils by a long shot. Nobody seems to have a problem except the kids who eat Tide pods, and they solved that with a zipper.

[kragen]

People who are handling chemicals whose lethal dose is less than a teaspoon need to understand the hazards involved. That is as true of common household chemicals like lye, sulfuric acid, and hydrochloric acid as it is for essential oils (though I would not describe any of those three as "everpresent").

However, it is worth noting that most household chemicals have a much larger lethal dose (are much less toxic) than commonplace essential oils! Such less-toxic chemicals include not only Tide Pods, but also everything else commonly used for laundry (even liquid bleach), window-cleaning ammonia, kerosene, unleaded gasoline, hair-bleaching-concentration hydrogen peroxide, most paint thinners, and even industrial degreasers like trisodium phosphate. I thought bleaching powder (calcium hypochlorite) was an exception, but I just looked up its LD50, and it's 850mg/kg orl-rat. So the lethal dose for an adult human is probably about 50 grams, which is an order of magnitude less toxic than oil of peppermint.

(Lye, sulfuric acid, and hydrochloric acid aren't toxic per se. You can safely add unlimited quantities of them to your food if they're dilute enough. But in reasonably concentrated forms they're corrosive enough to cause fatal injuries if ingested, even, potentially, at the teaspoon quantities we're talking about. Your mileage may vary, though, and you may just end up permanently maimed.)

It is possible that you don't appreciate just how small a quantity five grams is, or you have a vastly exaggerated idea of how dangerous commonplace household chemicals are. I have no idea how you could get to a dozen. Are you poisoning your rats with strychnine and sodium cyanide? There are much safer options now, you know. Most people stopped keeping those in their houses decades ago, even in poor countries.

(Yes, I edited my comment, just as you did, because I think it's important to make it a high-quality comment so that people who read it are not misinformed.)

[true_religion]

For the record, 5 grams is a teaspoon worth, and it’s pretty easy to accidentally splash that around if you’re pouring something.

Essential oils aren’t obviously caustic like bleach and since it’s food product someone might think that getting a little in their mouth or food they’ll eat is no big deal.

[hilbert42]

"Lye, sulfuric acid, and hydrochloric acid aren't toxic per se. You can safely add unlimited quantities of them to your food if they're dilute enough."

Right. Decades ago when I was in highschool and learning chemistry the chem teacher brought out reagent bottles of HCl, HNO3, H2SO4 and NaOH (in soln.) which he intended us students to smell and taste. He also had boxes of brand new test tubes and he issued everyone with four thereof for the demonstration/experiment which he insisted that we wash thoroughly under running water despite them being brand new.

His stated reasons were that as chemists that (a) we needed to become familiar with these common reagents as they were ubiquitous in chemistry labs and industry, and (b) we needed to know and experience the acidity of acids and to clearly distinguish them from the soapy character of the alkali. He also had a more important motive that I'll come to in a moment.

He then diluted the reagents to a safe level (I think it was about 1/40 Normal but I can't remember for sure). Then we students all lined up and he poured a few ml of each of the reagents into our test tubes for us to first smell then taste, which we all did.

Afterwards when we were all back in the tiered seats of the demonstration lab he made a statement in the sternest tone that shocked the wits out of lot of us:

"You're all dead!"

—long silent pause—

"Don't you ever do that again. You don't know whether the reagents are true to label, for all you know I could have given you poison and you'd be none the wiser until it was too late. And even if the bottles are true to label then you've still no idea how pure they are—they may contain impurities that are highly toxic."

He then went on to point out that these bottles of reagents were new and that he'd unsealed them in front of us and asked if anyone of us had noticed that.

He then pointed to print on the label that said BP—British Pharmacopeia grade and then to the assay list of impurities which were many decimal places below one percent (the minutest of a trace).

This chemistry lesson was by far the most important one we ever learned—nothing at university was ever the equal of it.

It's a great tragedy that these days health and safety rules preclude students from ever participating in such a demonstration. Students must be taught not to fear chemicals but nevertheless to treat them with care and great respect lest they bite.

These days much of society has an almost irrational fear of chemicals despite the widespread teaching of chemistry. That tells me there's something terribly wrong with the way we teach the subject—a matter that I've covered on HN previously.