Benzalkonium chloride is a mixture of quaternary benzyl dimethyl alkylammonium chlorides and a surfactant (removes dirt particles) cationic frequently used as antiseptics, to prevent bacterial growth, in healthcare and consumer products.
presented for the first time as antimicrobial agents by Domagk in 1935.

  It is used in:

• Restoration
• Home, medical and surgical disinfection
• Cleaning

It appears as a colourless liquid.

Disinfection

Benzalkonium chloride solutions for hospital use tend to be neutral to alkaline, non-corrosive on metal surfaces, non-staining, and safe to use on all washable surfaces. Is also added to drug products as preservative for multiple dose containers (1).

Benzalkonium chloride (BAK) is used as a preservative in several ophthalmic antiglaucoma agents. There are numerous reports on the effects of BAK on corneal epithelial cells in vitro (2).

Safety

In the package leaflet of a widely used eye drops, Vusumidriatic, in the Warnings and Precautions it is written: Benzalkonium chloride can also cause eye irritation especially if you have dry eye or discomfort to the cornea (the uppermost transparent layer of the eye). If you experience an abnormal feeling in the eye, burning or pain after using this medicine, talk to your doctor.

Benzalkonium chloride (BAK) is the most commonly used eye drop preservative. Benzalkonium chloride has been associated with toxic effects such as “dry eye” and trabecular meshwork degeneration, but the underlying biochemical mechanism of ocular toxicity by BAK is unclear. This study propose a mechanistic basis for BAK's adverse effects (3).

This 2020 study by Jingyi Wang et al. warns of the toxicity of benzalkonium chloride to the epithelial cells of the Meibomian gland, which secretes, via its ducts, the human tear film, a major source of lipids (4).

This study from 2022, although written by employees of a private company, is well documented and reaffirms that Benzalkonium Chloride, used in approximately 70% of ophthalmic formulations, is well known to cause cytotoxic damage to conjunctival and corneal epithelial cells, resulting in signs and symptoms of ocular surface disease (5).

Cosmetics

It is a restricted ingredient  V/54 and III/65  as a Relevant Item in the Annexes of the European Cosmetics Regulation 1223/2009

Antimicrobial agent. This ingredient is able to suppress or inhibit the growth and replication of a broad spectrum of microorganisms such as bacteria, fungi and viruses by making the stratum corneum temporarily bactericidal and fungicidal.

Antistatic agent. Static electricity build-up has a direct influence on products and causes electrostatic adsorption. The antistatic ingredient reduces static build-up and surface resistivity on the surface of the skin and hair.

Deodorant agent. When substances that give off an unpleasant odour are included in cosmetic formulations (typical examples are methyl mercaptan and hydrogen sulphide derived from garlic), deodorants attenuate or eliminate the unpleasant exhalation.

Preservative. Any product containing organic, inorganic compounds, water, needs to be preserved from microbial contamination. Preservatives act against the development of harmful microorganisms and against oxidation of the product.

Surfactant - Dispersing agent. Surfactant ingredient with cleaning properties that acts as a dispersing agent, capable of creating a barrier between particles by dispersing them and improving the separation between particles during the dispersion process. The particles undergo wetting, separation and then stabilisation of the suspension.

The most relevant studies on this ingredient have been selected with a summary of their contents:

Benzalkonium Chloride studies

• Molecular Formula: C₁₉H₃₄ClN
• Linear Formula C₆H₅CH₂N(CH₃)₂RCl (R=C₈H₁₇ to C₁₈H₃₇) 
• Molecular Weight: 311.938 g/mol
• CAS:  63449-41-2   68391-01-5   68424-85-1   85409-22-9  
• EC Number: 264-151-6    269-919-4    270-325-2    287-089-1 
• MDL number MFCD00145757
• Beilstein Registry Number 4062599

• Alkyldimethylbenzylammonium chloride
• Alkyl dimethyl benzyl ammonium chloride
• Benzyldimethyldecylammonium chloride
• Benzenemethanaminium, N-Decyl-N,N-Dimethyl-, Chloride
• Benzenemethanaminium, N-decyl-N,N-dimethyl-, chloride
• N-Capryl-N,N-dimethylbenzylammonium chloride
• Quaternary ammonium compounds, benzyl-C8-18-alkyldimethyl, chlorides
• Benzyl(decyl)dimethylammonium chloride
• Benzenemethanaminium, N-decyl-N,N-dimethyl-, chloride (1:1)
• C8-18-Alkydimethylbenzyl ammonium chlorides
• Benzyldimethyl(mixed alkyl)ammonium chloride
• decyldimethylbenzylammonium chloride
• Alkylbenzyldimethylammonium chlorides, benzyl-C8-18-alkyldimethyl
• decyldimethylbenzyl ammonium chloride
• N-Benzyl-N-decyl-N,N-dimethylammonium chloride
• benzyl-decyl-dimethylazanium chloride
• Ammonium, alkyl(C14-16)dimethylbenzyl-, chlorides
• benzyl-decyl-dimethyl-ammonium chloride
• Roccal

References_________________________________________________________________

(1) Ahn Y, Kim JM, Lee YJ, LiPuma J, Hussong D, Marasa B, Cerniglia C. Effects of Extended Storage of Chlorhexidine Gluconate and Benzalkonium Chloride Solutions on the Viability of Burkholderia cenocepacia. J Microbiol Biotechnol. 2017 Dec 28;27(12):2211-2220. doi: 10.4014/jmb.1706.06034.

(2) Berdy GJ, Abelson MB, Smith LM, George MA. Preservative-free artificial tear preparations. Assessment of corneal epithelial toxic effects. Arch Ophthalmol. 1992 Apr;110(4):528-32. doi: 10.1001/archopht.1992.01080160106043.

(3) Datta S, Baudouin C, Brignole-Baudouin F, Denoyer A, Cortopassi GA. The Eye Drop Preservative Benzalkonium Chloride Potently Induces Mitochondrial Dysfunction and Preferentially Affects LHON Mutant Cells. Invest Ophthalmol Vis Sci. 2017 Apr 1;58(4):2406-2412. doi: 10.1167/iovs.16-20903

(4) Wang J, Liu Y, Kam WR, Li Y, Sullivan DA. Toxicity of the cosmetic preservatives parabens, phenoxyethanol and chlorphenesin on human meibomian gland epithelial cells. Exp Eye Res. 2020 Jul;196:108057. doi: 10.1016/j.exer.2020.108057. 

(5) Goldstein MH, Silva FQ, Blender N, Tran T, Vantipalli S. Ocular benzalkonium chloride exposure: problems and solutions. Eye (Lond). 2022 Feb;36(2):361-368. doi: 10.1038/s41433-021-01668-x.