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benzalkonium chloride
also known as...
  • BAK
  • BAC
  • Really Bad Stuff
what it is

A very effective preservative. Problem is, it's just as good at killing healthy corneas as it is at killing bugs in the stuff it preserves.

Hence we consider it Really Bad Stuff, to be avoided by dry eye patients whenever possible.


Benzalkonium chloride is a chemical used as a preservative in many eyedrops, ranging from some over-the-counter eyedrops to many prescription eyedrops.

Chronic dry eye patients are generally advised to avoid frequent use of any eye lubricant products preserved with benzalkonium chloride, because of the damage it can cause to the tear film and ocular surface.

With respect to artificial tears, few remain on the market with BAK as the preservative because most doctors advise against its use and alternatives are readily available, including eyedrops with gentler preservatives and preservative-free unit-dose eyedrops.

With respect to prescription eyedrops such as glaucoma medications or even allergy drops, the situation is much more problematic because alternatives may not be readily available and the drug may be medically necessary. It is our hope that the ophthalmic pharmaceuticals will become more sensitive to this need and produce preservative-free versions of key topical ophthalmic preparations.

If you have been prescribed a drug containing BAK and expect to use it for more than a week, please discuss with your doctor whether there is a preservative-free version of the drug or whether there is an alternative equally effective drug without BAK that could be used to treat your condition.


Examples of over-the-counter eyedrops preserved with benzalkonium chloride:

  • Visine (several types)
  • Murine Tears
  • HypoTears
  • Akwa Tears
  • Moisture Eyes

I believe that NO over-the-counter lubricant should be preserved with BAK at all, because the people who need the lubricants are the very people who are most vulnerable to the harmful effects of BAK.

I believe that no OTC eyedrop of any kind should be preserved with BAK, because so many people using the OTC products are doing so without the supervision of a doctor who can warn them about the risks of overuse.

I believe that until unpreserved and/or more safely preserved Rx drugs (ranging from allergy drops to glaucoma drops) become available, doctors dispensing Rx drugs currently preserved with BAK should take steps to warn their patients about the risks of BAK and help guard their patients against overexposure.





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