Benzalkonium chloride

Benzalkonium chloride

}} Benzalkonium chloride, also known as alkyldimethylbenzylammonium chloride and ADBAC, is a mixture of alkylbenzyldimethylammonium chlorides of various even-numbered alkyl chain lengths. This product is a nitrogenous cationic surface-acting agent belonging to the quaternary ammonium group. It has three main categories of use; as a biocide, a cationic surfactant and phase transfer agent in the chemical industry.


Benzalkonium chloride is readily soluble in ethanol and acetone. Although dissolution in water is slow, aqueous solutions are easier to handle and are preferred. Solutions should be neutral to slightly alkaline, with colour ranging from clear to a pale yellow. Solutions foam profusely when shaken, have a bitter taste and a faint almond-like odour which is only detectable in concentrated solutions.


Standard concentrates are manufactured as 50% and 80% w/w solutions, and sold under trade names such as BC50, BC80, BAC50, BAC80, etc. The 50% solution is purely aqueous, while more concentrated solutions require incorporation of rheology modifiers (alcohols, polyethylene glycols, etc.) to prevent increases in viscosity or gel formation under low temperature conditions.


Applications are extremely wide ranging, from disinfectant formulations to microbial corrosion inhibition in the oilfield sector. It has been considered one of the safest synthetic biocides known and has a long history of efficacious use. It is currently used in human pharmaceuticals such as leave-on skin antiseptics, hygienic towelettes, and wet wipes. Ethanol-free benzalkonium solutions are often used for skin disinfection prior to withdrawing blood for blood alcohol content tests. Its use as a preservative in cosmetics such as eye and nasal drops attests to its general safety; however, there have been reports of allergy associated with continuous, long-term use in sensitive users, especially on mucous membranes.

Biological activity

The greatest biocidal activity is associated with the C12-C14 alkyl derivatives. The mechanism of bactericidal/microbicidal action is thought to be due to disruption of intermolecular interactions. This can cause dissociation of cellular membrane bilayers, which compromises cellular permeability controls and induces leakage of cellular contents. Other biomolecular complexes within the bacterial cell can also undergo dissociation. Enzymes, which finely control a plethora of respiratory and metabolic cellular activities, are particularly susceptible to deactivation. Critical intermolecular interactions and tertiary structures in such highly specific biochemical systems can be readily disrupted by cationic surfactants.

Benzalkonium chloride solutions are rapidly acting biocidal agents with a moderately long duration of action. They are active against bacteria and some viruses, fungi, and protozoa. Bacterial spores are considered to be resistant. Solutions are bacteriostatic or bactericidal according to their concentration. Gram-positive bacteria are generally more susceptible than Gram-negative. Activity is not greatly affected by pH, but increases substantially at higher temperatures and prolonged exposure times.

Newer formulations using benzalkonium blended with various quaternary ammonium derivatives can be used to extend the biocidal spectrum and enhance the efficacy of benzalkonium based disinfection products. This technique has been used to improve virucidal activity of quaternary ammonium-based formulations to healthcare infection hazards such as hepatitis, HIV, etc. Quaternary ammonium formulations are now the disinfectants of choice for hospitals. This is on account of user and patient safety even on contact with treated surfaces and the absence of harmful fumes. Benzalkonium 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.

The use of appropriate supporting excipients can also greatly improve efficacy and detergency, and prevent deactivation under use conditions. Formulation requires great care as benzalkonium solutions can be readily inactivated in the presence of organic and inorganic contamination. Solutions are incompatible with soaps, and must not be mixed with anionic surfactants. Hard water salts can also reduce biocidal activity. As with any disinfectant, it is recommended that surfaces are free from visible dirt and interfering materials for maximal disinfection performance by quaternary ammonium products.

Although hazardous levels are not likely to be reached under normal use conditions, it is important to remember that benzalkonium and other detergents can pose a hazard to marine organisms. Quaternary ammonium disinfectants are effective at very low ppm levels, so it is important to avoid excess in use. Responsible care ensures that the fragile marine ecosystems that sustain us are not disrupted.


Benzalkonium chloride is an allergen and several studies have cast doubt on its reputation for safety.

Some products have been reformulated in light of this research, but it is still widely used in eyewashes, hand and face washes, mouthwashes, spermicidal creams, and in various other cleaners, sanitizers, and disinfectants. Manufacturers of over-the-counter artificial tears and eye washes became concerned about chemical sensitivity from long-term daily use and have in some products substituted EDTA as a preservative. Some have added "for sensitive eyes" to labeling. There has also been concern that long-term use of benzalkonium as a preservative in nose sprays may cause swelling of mucosa and lead to rhinitis medicamentosa. Some manufacturers have put 3-day limits on safe use of such nose sprays.

A disinfectant containing benzalkonium chloride and the related compound didecyl-dimethyl ammonium chloride (DDAC) has been identified as the most probable cause of birth defects and fertility problems in caged mice.


Further reading

  • Bernstein IL: Is the use of benzalkonium chloride as a preservative for nasal formulations a safety concern? J Allergy Clin Immunol 2000 Jan; 105(1 Pt 1): 39-44.
  • Graf P: Adverse effects of benzalkonium chloride on the nasal mucosa: allergic rhinitis and rhinitis medicamentosa. Clin Ther 1999 Oct; 21(10): 1749-55.
  • Graf P, Hallen H, Juto JE: Benzalkonium chloride in a decongestant nasal spray aggravates rhinitis medicamentosa in healthy volunteers. Clin Exp Allergy 1995 May; 25(5): 395-400.

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