What Does Peracetic Acid Do and How Does It Work?

Peracetic acid is a powerful oxidizing disinfectant that destroys bacteria, viruses, fungi, and bacterial spores by chemically attacking the proteins and membranes that keep microorganisms alive. It is made by combining acetic acid (the main component of vinegar) and hydrogen peroxide, and it works across a remarkably wide range of settings, from poultry processing plants to hospital endoscopy suites to municipal wastewater systems. What makes peracetic acid particularly interesting compared to old standbys like chlorine is that it breaks down into water, oxygen, and acetic acid rather than forming the toxic chlorinated byproducts that have plagued water treatment for decades. That environmental friendliness, combined with genuine killing power, has driven a surge in adoption over the past two decades.

How Peracetic Acid Is Made

Peracetic acid, often abbreviated PAA, is produced through a reversible chemical reaction between acetic acid and hydrogen peroxide, typically with a small amount of sulfuric acid acting as a catalyst.¹ Because the reaction runs in both directions, commercial PAA solutions are always an equilibrium mixture: they contain PAA alongside leftover hydrogen peroxide, acetic acid, and water. You never get a bottle of pure peracetic acid. Concentrated solutions typically range from about 5% to 15% PAA, with the rest being the equilibrium partners.

This equilibrium chemistry matters for practical use. Over time, or at elevated temperatures, PAA in a solution can decompose back into its starting materials. Storage conditions, temperature, and the ratio of ingredients all affect how long a prepared solution stays potent. The instability is both a drawback (you have to manage shelf life carefully) and a benefit (once PAA has done its job, it does not persist in the environment the way some other disinfectants do).

Researchers have recently been exploring ways to generate PAA on demand using electricity rather than mixing chemicals in a factory. One approach uses specialized carbon electrodes to produce hydrogen peroxide in place and then immediately convert it to PAA, avoiding the need to store and ship concentrated solutions.² A related method uses gas diffusion electrodes to synthesize various peracids, including PAA, from renewable electricity.³ These technologies are still in development, but they could eventually allow facilities to produce PAA on-site and on demand, sidestepping the hazards of transporting concentrated solutions.

How It Kills Microorganisms

PAA is an oxidizer, meaning it rips electrons away from the molecules it contacts. When it meets a bacterial cell or a virus particle, it goes after the chemical bonds that hold critical biological structures together. The primary targets are sulfur-containing amino acids in proteins, particularly cysteine and methionine, along with histidine. Research on amino acid oxidation has shown that cysteine reacts extremely rapidly with PAA, while methionine and histidine react at measurable but still meaningful rates.⁴ Most other amino acids barely react at all, which means PAA is not indiscriminately chewing through every molecule it touches. Instead, it is selectively hitting the chemical groups that microorganisms rely on for enzyme function, membrane integrity, and signal transduction.

The practical result of this targeted oxidation is that PAA disrupts proteins and lipids in cell membranes, damages essential enzymes inside the cell, and ultimately causes the cell to lose its ability to maintain itself and reproduce. Viruses, which lack the protective cellular machinery that bacteria have, are similarly vulnerable because PAA can denature the proteins in their outer capsid or envelope. Animal studies have confirmed that exposure to PAA triggers oxidative damage in tissues, consistent with its mechanism of attacking biological molecules through peroxidation.⁵

One reason PAA is effective against such a wide range of organisms is that the targets it hits, sulfur-rich amino acids and lipid membranes, are universal features of life. There is no easy way for a microorganism to evolve around the need for cysteine in its enzymes or lipids in its membrane, which limits the risk of resistance developing. That said, the resistance question is not fully settled, particularly in the food industry where bacteria face PAA exposure repeatedly.

What It Works Against

PAA’s antimicrobial reach is broad. It is effective against vegetative bacteria (the actively growing forms), bacterial spores (the dormant, heavily armored forms that survive most other disinfectants), viruses (both enveloped and non-enveloped types), and fungi. This versatility is a major selling point.

Bacterial spores are generally the hardest targets for any disinfectant, and PAA handles them well under the right conditions. A study on sporicidal activity found that PAA in gaseous form achieved a six-log reduction, meaning it killed 99.9999% of spores on cloth carriers, within 90 minutes when humidity was high. When humidity dropped, performance fell sharply to only a two-log reduction at comparable concentrations, demonstrating that environmental conditions matter as much as the chemical itself.⁶

Against viruses, PAA has proven effective in both liquid and vapor form. In one fogging study, PAA eliminated reovirus, parvovirus, and polyomavirus from glass surfaces in laboratory conditions, with log reductions ranging from about 6.4 to 9.0 depending on the virus, meaning no detectable infectious virus remained.⁷ Non-enveloped viruses, which are generally tougher to kill than enveloped ones, are also susceptible. Research on chemical inactivation has found that feline calicivirus, murine norovirus, adenovirus, and poliovirus all respond to PAA treatment, though hepatitis A virus appears somewhat less susceptible than poliovirus.⁸

Biofilms present a more nuanced challenge. PAA combined with hydrogen peroxide can inactivate nearly all bacterial cells in a biofilm within minutes. However, research has shown that the matrix surrounding biofilm cells may actually increase in mass after treatment, and surviving cells can regrow and restore the biofilm within a day.⁹ This suggests that while PAA is excellent at killing individual cells, biofilm management requires repeated application or combination strategies to prevent regrowth.

Where Peracetic Acid Gets Used

PAA has carved out major roles in food processing, healthcare, and water treatment. Each application takes advantage of slightly different properties, but they all rely on the same oxidative killing mechanism.

Food Processing

In the United States, PAA is widely used in poultry processing as an antimicrobial wash applied to carcasses and equipment to reduce pathogens like Salmonella. It is one of several approved biocides, and the industry has explored using it in combination with other antimicrobials such as cetylpyridinium chloride, calcium hypochlorite, and sodium hypochlorite to achieve better results than any single agent alone.¹⁰ The question of whether repeated PAA exposure drives Salmonella toward resistance is an active area of research.¹¹

For fruits and vegetables, PAA is authorized under federal regulations for post-harvest use at concentrations between 0.005% and 2%. It can also be used on raw and cooked meat, including poultry, under separate regulatory provisions.¹² These low concentrations are enough to reduce pathogen loads on food surfaces without leaving harmful residues.

Healthcare and Endoscope Reprocessing

Hospitals use PAA for high-level disinfection of instruments that cannot withstand traditional steam sterilization, particularly flexible endoscopes. These instruments are complex, with narrow internal channels that harbor bacteria if not properly cleaned. A study comparing PAA-based reprocessing to glutaraldehyde and ortho-phthalaldehyde found that PAA left significantly fewer residual bacteria on endoscope surfaces, and it proved effective against antibiotic-resistant organisms including MRSA, vancomycin-resistant enterococcus, and Clostridioides difficile.¹³ PAA also works faster than glutaraldehyde, which typically requires longer soak times to achieve the same level of disinfection.

How PAA Compares to Chlorine

The most common comparison is between PAA and chlorine-based disinfectants, since chlorine remains the default in many water treatment and food processing systems. The two are not identical in performance, and each has advantages depending on the situation.

In fresh-cut vegetable processing, a study conducted at industrial scale found that PAA and chlorine performed similarly in terms of antimicrobial activity in the wash water. The critical difference was what happened as organic matter built up. Chlorine’s effectiveness dropped as organic material accumulated in the washing water, while PAA’s killing power remained constant regardless of the organic load.¹⁴ For a processing plant running all day, this stability is a meaningful advantage since the wash water gets progressively dirtier as the shift goes on.

In wastewater disinfection, however, a comparative study found that at similar doses, sodium hypochlorite (chlorine bleach) was actually more effective than PAA, and chlorine’s action was less affected by contact time.¹⁵ This means PAA is not a straight upgrade from chlorine. In clean water with controlled contact times, chlorine may outperform PAA. Where PAA shines is in dirtier, more variable conditions and in situations where chlorinated byproducts are a concern.

That byproduct question is important. Chlorine reacts with organic matter in water to produce trihalomethanes and haloacetic acids, compounds linked to health risks at chronic exposure levels. PAA generally produces far fewer of these halogenated byproducts in normal domestic wastewater.¹⁶ However, there is an important exception: in high-salinity water, such as the ballast water carried by ocean-going vessels, PAA can actually produce more brominated and iodinated byproducts than chlorine during extended treatment.¹⁶ This occurs because PAA oxidizes bromide and iodide ions present in salt water into reactive forms that then combine with organic matter to form harmful compounds.

The Disinfection Byproduct Problem in Salty Water

The finding that PAA can generate problematic byproducts in bromide-rich water deserves attention because it complicates the narrative that PAA is simply the “green” alternative to chlorine. In typical municipal wastewater with low halide content, PAA produces minimal halogenated byproducts, and the assumption that PAA is cleaner than chlorine holds. But in waters containing elevated bromide, the chemistry changes substantially.

Research has shown that during PAA disinfection of bromide-containing water, various brominated byproducts form within the first couple of hours and continue to accumulate. The most abundant byproduct observed was dibromoacetic acid, which in some conditions accounted for over 80% of the total organic bromine from known byproducts. The detected known byproducts represented only a fraction, sometimes as low as about 5%, of the total organic bromine formed, indicating that many unknown brominated compounds were also being created.¹⁷ This is a significant finding for applications like ballast water treatment, industrial cooling systems using brackish water, or any scenario where the water being treated contains significant salt content.

Performic acid, a close chemical relative of PAA, does not appear to share this weakness. Studies comparing the two found that performic acid controlled all tested byproducts during long-term disinfection of saline water, even as PAA was generating elevated levels of brominated and iodinated compounds.¹⁶ This distinction may eventually influence which peracid gets chosen for which application.

Safety, Exposure Limits, and Corrosion

PAA is not gentle on people or on materials. Concentrated solutions are corrosive and highly irritating to the eyes, skin, and respiratory tract. For workers who handle PAA regularly, the most sensitive concern is airway irritation from inhaling vapors. A review of animal and human toxicity data concluded that sensory irritation of the respiratory tract is the key endpoint for setting workplace limits. Based on the data, a time-weighted average exposure limit in the range of roughly 0.1 to 0.2 parts per million was recommended, with short-term exposure limits around 0.4 to 0.5 ppm.¹⁸ These are low thresholds, reflecting how irritating even small airborne concentrations can be. In practice, this means proper ventilation, respiratory protection, and automated dosing systems are standard in facilities that use PAA at scale.

Corrosion is the other major practical concern. PAA’s oxidizing nature attacks metals, particularly common grades of stainless steel, copper, brass, and aluminum. Research on stainless steel corrosion found that standard grades like 316L and 317L corroded significantly in PAA solutions, especially when chloride was present. Higher-molybdenum alloys like 254SMO and 654SMO showed much better resistance across all conditions tested.¹⁹ For facilities choosing equipment, this means that the cheaper stainless steels used in most standard plumbing and food processing equipment may not hold up to regular PAA exposure.

There are ways to mitigate the corrosion problem. Research into corrosion inhibition found that unmodified acidic PAA solutions caused strong surface damage across a range of materials, including aluminum, copper, brass, stainless steel, PVC, wood, and ceramics. However, adjusting the solution’s pH to neutral reduced damage considerably, and adding a nonionic surfactant as a corrosion inhibitor eliminated observable corrosion entirely on the materials tested.²⁰ These modifications could make PAA more practical for applications where it contacts sensitive materials, though they add complexity and cost to formulation.

Regulatory Status in Food Applications

In the United States, PAA has achieved generally recognized as safe (GRAS) status for use on food at concentrations between 0.005% and 2%. Under federal regulations, it is authorized for use on fruits and vegetables that are not classified as raw agricultural commodities (meaning produce that has undergone some processing, like washing and cutting), and separately on raw and cooked meat and poultry.¹² The European Union has approved PAA for certain food contact applications as well, though regulatory frameworks differ between countries in terms of permitted concentrations and specific uses.

The permitted concentration range is worth noting because it is quite wide. At the low end, 0.005% (50 ppm) is a dilute rinse suitable for produce. At the high end, 2% (20,000 ppm) is a powerful antimicrobial wash for meat. The appropriate concentration depends on the target pathogen, the contact time, and the food product involved. Using more PAA than necessary is not just wasteful; it can affect the sensory qualities of food (particularly taste and smell, since acetic acid is one of the breakdown products) and raises worker exposure concerns.

The Resistance Question in Poultry Processing

One of the more pressing open questions about PAA is whether repeated use in food processing could select for resistant bacteria. This is not a theoretical concern. In poultry plants, carcasses pass through PAA-treated water at multiple stages, creating sustained selective pressure on whatever Salmonella or other pathogens survive each treatment step. A review of the evidence on PAA in poultry processing specifically flagged resistance development as an emerging area of interest, noting that while PAA offers clear advantages over traditional disinfectants, the possibility of Salmonella populations adapting to tolerate it deserves ongoing monitoring.¹¹

The oxidative mechanism of PAA makes classical resistance (like the kind bacteria develop against antibiotics through single gene mutations) less likely but not impossible. Bacteria can upregulate stress-response pathways, increase the production of antioxidant enzymes, or alter their membrane composition to better withstand oxidative attack. Whether these adaptive responses translate to clinically meaningful resistance at concentrations used in processing plants is still being studied. The combination approach, applying PAA alongside other biocides with different mechanisms, is one strategy being explored to stay ahead of any potential adaptation.¹⁰

1
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