Does chlorhexidine really become ineffective after its expiry date?

This morning, I applied some chlorhexidine on a patch of scratched skin that I had previously washed with some soap and water.

After I had done so, I remembered that the bottle had sat on the shelf for a long time (I was not at home so I used what I found - I tend to be very careful with expiry dates). I checked the label and indeed, it had expired exactly a year ago (manufactured: 02/2011 expires: 02/2014). I’m not particularly worried about it since it was a minor wound that had been cleaned but I wonder if the product had completely lost its potency. Seems unlikely to me. Less effective, probably but completely useless? I don’t think so.

I didn’t even know that chlorhexidine was used as a topical antiseptic. (I use 91% isopropyl myself.) I use chlorhexidine as an antibacterial mouth rinse. What I wonder is: Is it really more effective at killing all those big bad oral germs, compared to OTC mouthwashes like Listerine or Scope?

It matters because chlorhexidine is available by prescription only and I have to badger my dentist every time I need a refill, not to mention that it costs me something like $30 a bottle, and that’s just my co-pay. I think it costs vastly more than that if one has to pay the full cost out-of-pocket.

According to Wikipedia, chlorhexidine stays activated in the mouth longer than other typical ingredients. My dentist advised it, though I can never quite tell if they’re trying to push something on me or not.

You can get chlorhexidine mouthwash on eBay for reasonably cheap. I’m a little surprised they don’t block it but I guess it doesn’t quite qualify as a medication.

You can legally get a gallon of chlorhexadine solution on for only $13.99.

The big difference is that the gallon is more concentrated than your mouthwash and it is labeled for veterinary use only.

Chlorhex is the go-to disinfectant in veterinarians’ offices. They use it to treat the animals and to clean up the exam room and instruments between patients. And I’m sure they pay less than $13.99 a gallon.

I do not know if there is any substantive difference between veterinary-grade chlorhex and human mouthwash-grade chlorhex or if this is one of the many cases where they slap a “human use” label on a cheap product and mark up the price by 1000%. So use at your own risk.


That really is more concentrated. The page you linked says it’s a 2% solution. The prescription oral rinse is a 0.12% solution. One would have to do some DIY mixing (not to mention some algebra) to deal with that. And I’ll bet it doesn’t have the vaguely minty flavor either.

Thanks for the answers, Dr. Strangelove and Alley Dweller. Don’t forget the OP’s question too, about potency after the expiration date. Didn’t mean to hijack.

Funny, it’s the other way around for me: I used it as a topical antiseptic for years before I learnt that it was also sometimes added to mouth rinse. Perhaps it’s a Europe / US thing.

Anyway, as a topical antiseptic, it’s my top choice as it’s safe both for adults and children, odourless, colourless (no stains on clothes) and doesn’t sting when you apply it. After years of using it, I’d say it’s very effective, too.

I’ve checked the scratch this morning and it looked fine. As I said, it was not really a matter of concern, just curiosity.

I’m sure it’s just fine for home use. I wouldn’t trust it for surgical prep at work past the expiry, but I wouldn’t throw it out, just use it for non-sterile cleaning and hand washing.

I did find this document, which says:
Aqueous solutions of chlorhexidine salts may decompose to produce trace amounts of 4-chloroaniline; decomposition is increased by heating and alkaline pH conditions. 4-chloroanilinegave equivocal evidence of carcinogenicity in bioassays carried out by the US NCI in Fischer 344 rats and B6C3F1 mice.

That’s mildly concerning, but it seems to be really low levels. There’s also this MSDS, which says:
Chemical Stability: Stable under recommended storage conditions.

Safe storage conditions are:
Keep container tightly closed in a dry, well ventilated location. Store at 2- 8 °C. Product is light sensitive.

So probably cooler than you’ve stored it under unless you keep it in the fridge. Still, even at 20-25 C I’d be shocked if there were much of a difference. The light sensitivity is not too surprising; if you kept it out of direct sunlight I’d imagine that’s not a problem either.

Thanks for the answers.

The bottle was in a closed cupboard. Apart from that, I don’t know whether it’s been stored properly since it was not in my home but in a work environment. It’s likely that the solution has been used relatively often as it’s a pretty busy place and minor wounds are probably a weekly occurence.

I’d just get the6 oz bottle of the 4% human-wound use kind ($5.99), and just replace it every couple of years.

Beyond that, Hibiclens is available at every drugstore I’ve ever been in, and most usually have a house-brand version as well. Hardly tough to find!

That stuff has fragrances and stuff though–not great if you’re diluting for mouthwash use. It’s hard to tell, but I don’t think the gallon-size jug has the extra stuff.

The OP was talking about using it on an abrasion as an antiseptic- that’s pretty much what Hibiclens is made for.

I wouldn’t want to use it as a mouthwash though. The most interesting thing about it to me, is that apparently if you use it as a hand washing soap, it has strong residual antibacterial action for hours after you wash your hands with it.

Understood; I was just commenting for those considering it for mouthwash.

That’s what makes it so good for mouthwash. Listerine and others don’t have time to do much in the minute or two you spend swishing it around. Chlorhex keeps working. My dentist said I shouldn’t eat or drink anything for an hour or so after using it for maximum effect.

But like Senegoid said, it’s expensive (even the cheaper one I linked to was ~$17/bottle). So I only used a bottle or two when the dentist told me to. If I can add a couple ounces of bulk 2% solution to a bottle of Listerine, that’s possibly a cheap way of getting the same thing.

Maybe chlorhexidine keeps working because you keep it in your mouth longer. The instructions are: Rinse mouth with it for 30 seconds. Then spit it all out, but don’t rinse with water for 30 MINUTES. (You’re also not supposed to swallow the stuff. So for 30 minutes you try not to swallow at all.)

Would Listerine or Scope work as well if it were used that way too?