What are quaternary ammonium disinfectants?

Last updated: October 2026

Quaternary ammonium compounds (quats) are positively charged surfactant disinfectants, such as benzalkonium chloride (ADBAC) and DDAC, that kill germs by disrupting cell membranes and viral envelopes. On clean surfaces they control many bacteria and enveloped viruses, but they are weak against spores, mycobacteria and non-enveloped viruses, and manure, soap residue and hard water inactivate them.

What are quaternary ammonium compounds?

Quaternary ammonium compounds, often shortened to quats or QACs, are a category of human-made chemicals used to control bacteria, viruses and other germs on surfaces¹. Chemically they are cationic, or positively charged, surfactants². In the United States they are antimicrobial pesticides: more than 2,000 registered pesticide products contain quats, and the first quat antimicrobial pesticide was registered in 1947¹.

The US Environmental Protection Agency (EPA) groups quats into four categories by structure¹. Two of these groups are the alkyl dimethyl benzyl ammonium chloride (ADBAC) group of 24 similar chemicals, which is sometimes called benzalkonium chloride, and the didecyl dimethyl ammonium chloride (DDAC) group of five¹. Disinfectants sometimes contain more than one quat¹. Later product generations are generally more germicidal, less foaming and more tolerant of organic load and soaps².

How do quats kill germs?

Quats break open the membranes of bacteria and the outer coatings of enveloped viruses, and breaking the membrane kills the cell¹. At the molecular level they bind irreversibly to the negatively charged phospholipids in bacterial membranes and denature membrane proteins, which destroys the membrane's control over what passes through².

This takes time. How long depends on the quat and its concentration, and some quats must stay in contact with a germ for minutes¹. The label states the contact time, the period a surface must stay visibly wet for the product to work¹. Some products also leave surfaces bacteriostatic for a brief period after use². Quats work best at neutral to alkaline pH, with the greatest efficacy at pH 9 to 10, and they lose activity below pH 3.5².

What do quat disinfectants kill, and what do they miss?

Quats have a narrower spectrum than oxidizing disinfectants. EPA defines a disinfectant as a product that destroys or irreversibly inactivates infectious fungi and bacteria on surfaces but not necessarily their spores⁴, and the organisms a specific quat product controls are those listed on its label¹.

Why do quats fail in barns, coops and footbaths?

Dirt is the main reason. Quats are easily inactivated by organic material and by anionic soaps and detergents, and hard water reduces their activity because calcium and magnesium ions form complexes with the disinfectant². Manure, bedding and feed can also hide organisms and react with a disinfectant in place of the microbes².

A study of boot baths using boots soiled with pig manure showed how much this matters. When boots carried pig manure, the type of disinfectant made no difference; a contaminated bath added contamination to boots; and boots that were scrubbed free of manure and then soaked for 5 minutes in a quat bath met the standard for disinfection⁵.

In-use solutions can also become a source of bacteria. A 2023 review reports that disinfectants with a quat as the sole active ingredient are more likely than other types to become contaminated with Gram-negative bacteria, and that Serratia marcescens recovered from contaminated footbaths on several dairy farms survived a fresh in-use concentration of benzalkonium chloride³. The same review notes that cotton and microfiber cloths absorb quats from buckets, lowering the working concentration³.

How do you use a quat disinfectant on a farm or in a kennel?

Cleaning first is not optional with quats. A university animal health center's cleaning and disinfection guidance sets out the order²:

• Remove visible manure, bedding, feed and debris by scraping, brushing or sweeping².
• Wash with soap or detergent and water, then rinse well, because soap residue can inactivate some disinfectants².
• Let surfaces dry so leftover water does not dilute the solution².
• Mix fresh solution daily or as the label specifies, at the label concentration; stronger is not always better². Always follow the product label.
• Keep surfaces wet for the full label contact time, then rinse items thoroughly before animals return, especially feed and water equipment².
• Clean and dry reusable buckets before adding new disinfectant, and check the in-use concentration after dilution³.
• For footbaths, scrub manure off boots first and keep the bath itself clean⁵.

Are quats hazardous to people, animals and the environment?

Concentration drives the hazard. Quats are low in toxicity through the skin but can be severely irritating or corrosive to skin and eyes depending on the concentration, and they are moderate in toxicity when inhaled or swallowed¹. Several studies found asthma more common in workers who used quat cleaning products¹. An animal health guide adds that quats are highly toxic if ingested, so disinfected areas and items should be rinsed after the contact time and before animal use².

Quats bind tightly to soil and sediment, which limits their movement into groundwater¹. They are toxic to aquatic animals, particularly fish, so runoff into ponds, streams and drains should be avoided²; ADBAC is classed as highly toxic to fish and to aquatic invertebrates¹.

Resistance is a real but bounded concern. Laboratory studies show bacteria can develop tolerance to quats, and several studies link benzalkonium chloride tolerance with antibiotic resistance³. A 2023 review concluded that there is insufficient real-world evidence that frequent quat use has driven widespread antibiotic resistance, and that in-use concentrations are often far above the levels bacteria tolerate in the lab³. The review calls for closer attention to correct use to prevent contamination of quat disinfectants³.