Sanitizers and disinfectants are important tools for reducing the spread of disease-causing germs. However, temperature can impact how well these products work. This article explores how temperature affects the effectiveness of various sanitizers and disinfectants.
How do sanitizers and disinfectants work?
Sanitizers and disinfectants work by damaging or destroying germs through chemical reactions. When these products are applied to surfaces or skin, they interact with proteins and lipids in the outer membranes of microbes, disrupting their structure and killing them or stopping them from reproducing and spreading.
Some common active ingredients in sanitizers and disinfectants include:
- Alcohols like ethanol and isopropanol
- Chlorine compounds like sodium hypochlorite (bleach)
- Quaternary ammonium compounds (QUATs)
- Hydrogen peroxide
The mode of action depends on the specific active ingredient. For example, alcohols denature proteins while bleach oxidizes cell components. But in all cases, these chemicals need to physically interact with and penetrate cells to inactivate pathogens.
How does temperature impact chemical reactions?
Temperature can significantly influence how quickly and effectively sanitizers and disinfectants work. Chemical reactions tend to speed up at higher temperatures and slow down at lower temperatures. There are a few reasons for this effect:
- Higher temperatures give molecules more kinetic energy and motion, allowing them to interact and react more frequently.
- Heat lowers activation energy barriers for reactions, so fewer molecular collisions are needed for reactions to occur.
- Increased molecular motion at higher temperatures better facilitates mixing and contact between reagents.
The specific impacts depend partly on the ingredients involved. But in general, the kinetics of the key reactions that damage or destroy pathogens will be enhanced at higher temperatures.
Effect of low temperatures on sanitizers
Using sanitizers and disinfectants at temperatures lower than room temperature can significantly reduce their germ-killing effectiveness. For example, one study found that 70% ethanol and 0.5% hydrogen peroxide sanitizers were markedly less effective against a virus when used at 4°C compared to 22°C.
Cooler temperatures likely slow down the reactions these chemicals use to damage viral proteins and lipids. This gives pathogens more of a chance to survive and remain infectious.
Another investigation looked at how temperature impacts the activity of bleach, a QUAT, and pine oil disinfectant against Listeria bacteria. At 4°C, it took substantially longer exposure times for each chemical to produce a 4-log reduction in Listeria numbers compared to 20°C or 45°C.
| Disinfectant | Time for 4-log reduction at 4°C | Time for 4-log reduction at 20°C | Time for 4-log reduction at 45°C |
|---|---|---|---|
| Bleach | 90 minutes | 5 minutes | Less than 1 minute |
| QUAT | 24 hours | 5 minutes | Less than 1 minute |
| Pine oil | 3 hours | 10 minutes | Less than 1 minute |
Clearly, carrying out disinfection at refrigerator-like temperatures impairs antimicrobial performance. The researchers suggested the extreme temperature slows down chemical inactivation of bacteria.
Impacts on alcohol sanitizers
Alcohol-based hand sanitizers are commonly used to disinfect skin and surfaces. However, the biocidal efficacy of alcohols can decrease substantially at cool temperatures. For example:
- One study found that ethanol and isopropanol were significantly less able to inactivate poliovirus at 4°C compared to 20°C.
- Experiments on hepatitis A virus showed 70% ethanol was ~100x less effective when used at 4°C vs 20°C.
- Research on wipes containing 60% ethanol or isopropanol demonstrated reduced activity against a norovirus surrogate at 6°C compared to 20°C.
The reduced antiviral effects parallel slower inactivation of bacterial species like E. coli and S. aureus by alcohols at cooler vs normal room temperatures.
Lower temperatures likely contribute to reduced sanitizer effectiveness through slower kinetics of alcohol denaturation of pathogen proteins and membranes. Colder solutions may also evaporate more slowly off surfaces.
Impacts on hydrogen peroxide
Hydrogen peroxide works by producing destructive hydroxyl radicals that damage proteins, cell membranes, and DNA. However, experiments indicate hydrogen peroxide disinfectants become less effective at lower temperatures:
- 0.5% hydrogen peroxide killed poliovirus more slowly at 4°C compared to 20°C.
- Solution temperature impacted the virucidal activity of a 1.4% hydrogen peroxide soak against swine viruses.
- Hydrogen peroxide wipes had reduced efficacy against C. difficile spores at 6°C vs 20°C.
The thermal sensitivity likely arises because lower temperatures slow down the decomposition of hydrogen peroxide into free radicals. This reduces the oxidative damage that kills microorganisms.
Impacts on chlorine compounds
Hypochlorites like bleach are commonly used for disinfection. However, lower temperatures can reduce the microbicidal effects of chlorine solutions. For example:
- Sodium hypochlorite solution was less effective at inactivating hepatitis A virus at 4°C compared to 20°C.
- In experiments with E. coli, antiseptic chlorhexidine was 14x less effective at 0°C compared to 35°C.
- Cooling chlorinated recreational water from 27°C to 22°C reduced inactivation of Cryptosporidium.
The antimicrobial activity of chlorine stems from irreversible oxidation of proteins, membranes, and other cell components. This explains why lower temperatures that slow chemical reactions would reduce chlorine efficacy.
Effects of high temperatures on sanitizers
In some cases, very high temperatures can also impact the performance of disinfectants:
- Bleach solutions may lose chlorine content faster through evaporation at high temperatures.
- Peracetic acid degrades more quickly at elevated temperatures, reducing biocidal activity.
- High heat can evaporate alcohol prematurely before it achieves full antimicrobial effect.
However, the evidence suggests sanitizers and disinfectants tend to work better at mildly elevated temperatures up to about 45°C. For example, higher temperatures generally increase the efficacy of alcohols, chlorine, and QUATs.
The optimal temperature often depends on the specific sanitizer and use case. But in most situations, cool temperatures below room temperature will impair antimicrobial activity.
Effect of water temperature on handwashing efficacy
Handwashing with soap and water is important for reducing pathogen transmission. Research indicates the temperature of the water used can impact handwashing efficacy.
Washing hands with warmer water generally removes more microbes from skin. For example:
- Washing with 40°C water reduced bacteria on hands more than 15°C or 25°C water in one study.
- Another investigation found that water at 15°C removed only 42% of microbes from hands vs 77% removal at 40°C.
Possible reasons that warmer water enhances handwashing efficacy include:
- Higher temperatures help dissolve skin oils and detach microbes.
- Warmer water may cause more skin friction during washing.
- Heat helps kill some microbes and prevent transfer back to hands.
However, very hot water above 54°C can damage skin with prolonged exposure. Balance is needed to optimize handwashing while preventing scalding.
Tips for maximizing sanitizer efficacy in cool temperatures
If using sanitizers or disinfecting in a cool environment, here are some tips to counteract reduced performance:
- When possible, warm sanitizing solutions before application.
- Insulate containers during longer contact times to retain heat.
- Increase contact time to account for slower inactivation kinetics.
- Use maximum label concentrations of active ingredients.
- Choose sanitizers less prone to thermal effects like QUATs.
For handwashing, use the warmest comfortable water. Pre-warming rinse water can help maximize efficacy.
Proper sanitization is crucial for infection control in food service, healthcare, and other industries. Understanding how low temperatures affect disinfectants can help optimize protocols across settings.
Conclusion
Temperature has a significant impact on the antimicrobial efficacy of chemical sanitizers and disinfectants. Cooler temperatures below room temperature generally reduce the effectiveness of products like alcohols, bleach, hydrogen peroxide, and QUATs. Colder solutions slow down the chemical reactions responsible for inactivating microbes on surfaces and skin.
Conversely, warmer water can enhance handwashing efficacy by better dissolving oils and detaching more pathogens. However, very high temperatures may impair certain disinfectants through evaporation or chemical instability.
When using sanitizers in cool environments, try warming solutions, insulating containers, extending contact times, or selecting less temperature-dependent actives. Adjusting protocols based on temperature effects can help maximize germ reduction.