[ghporter]

Without going into too much detail for background, it’s pool season so it’s time to mix a batch of “ear drying drops” to ward off swimmer’s ear. This is half 70% isopropyl alcohol and half 5% vinegar. The vinegar acidifies the ear canal to kill bacteria, and the alcohol dissolves any water, allowing it to either quickly evaporate or drip out with the head tilted.

But there’s another DIY ear drop for addressing stubborn ear wax, made of half 70% alcohol and half 3% hydrogen peroxide. Again, the alcohol helps keep the drops from staying around for too long, and the peroxide works to break up the wax.

Here’s where I’m going: supposedly making an “combination ear drying and ear wax drop” with the above components is Very Very Bad. The acetic acid and the hydrogen peroxide react to produce paracetic (or peroxyacetic) acid.

Internet randos have posted horror stories about the dangers of paracetic acid which “in its concentrated form it is highly corrosive and unstable” (per the USDA) (emphasis mine).

But…. (Here’s the chemistry part.) If I put 10ml of 5% acetic solution in a container with 10ml of 3% hydrogen peroxide solution, that’s 19.2ml of water and 0.8ml of “reactants”. Just how dangerous/unstable/corrosive is 0.8ml of paracetic (peroxyacetic) acid in 19.2ml of water?

[reader50]

I buy off-the-shelf earwax removal drops, rather than test home chemistry. They're labeled as "carbamide peroxide 6.5%".

It's been a long time since chem class. But testing how strong an acid is, by dripping it into one ear is definitely the way to go. If it's too strong, you always have the spare ear.

[ghporter]

Yeah, I wasn’t so much worried about saving money by brewing this stuff up, but rather wondering how much truth was behind these randos’ claims. And no, I don’t want to get into any reaction equations or molarity. I just wondered how whack the claims were.

[dav]

doesn't hydrogen peroxide kill bacteria as well, rendering the vinegar unnecessary?

[ghporter]

H2O2 breaks down cell walls - and it doesn’t care if they’re bacteria or your own cells. It takes 5 minutes of contact with the bad guys for peroxide to effectively kill bacteria. The vinegar would alter the pH enough to either out-right kill the most damaged bacteria or shut down the rest of them.

Swimmer’s ear happens when water remains in the ear canal long enough for bacteria to multiply and cause inflammation. “Ear drying drops” are either alcohol and vinegar or alcohol and peroxide. As I noted above, the alcohol makes remaining water evaporate more quickly, and the vinegar lowers the pH enough to discourage bacteria - often simply killing whatever bacteria came from the water you swam in. In mixtures with peroxide instead of vinegar, the peroxide is the antibacterial agent, but it also kills naturally occurring “good” bacteria, and if left in place for too long it can irritate the lining of the ear canal (which often causes excess wax production in response).

A typical swimmer’s ear situation is caught early and treatment with milder (vinegar) solutions works well.

Enter the ear wax loosening formula. The peroxide tends to loosen wax from the ear canal - probably by breaking down canal cells as well as altering the chemical properties of the cerumen (wax) which is about 60% dead skin cells, with the rest being various long-chain fatty acids, alcohols and cholesterol. All of these constituents are susceptible to the oxidizing effects of peroxide. Honestly, if warm water soaking and an alcohol/peroxide soak doesn’t loosen your ear wax enough to make a difference, you should see an ear specialist.

I had completely discounted actually making a “drying and wax removing” formula long ago. I just remembered how many Google hits about mixing vinegar and peroxide I’d seen, and how vehement they were about how horrible it would be to even try doing it. But this post on the American Chemical Society’s community forum goes through the actual chemical equations and shows that mixing 5% household vinegar and 3% hydrogen peroxide can produce “just enough peracetic acid to provide some extra antiseptic activity”. An actual chemist on an actual chemistry forum pointing out that it actually won’t end the world, or even hurt anything (except bacteria) much, if you mix these materials! Thanks for shutting down the randos, at least for me.