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Also called: Cold sterilization, Chemical sterilisation, High-level disinfection

Cold Sterilisation vs Autoclave: When a Chemical Soak Is Enough

Soaking instruments in a chemical is not the same as autoclaving them. What cold sterilants and high-level disinfectants can and cannot do, and where each belongs.

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What “cold sterilisation” means

“Cold sterilisation” is an old name for immersing instruments in a liquid chemical at room temperature. The same chemicals are used in two very different ways: a shorter soak for high-level disinfection, which kills all microorganisms except large numbers of bacterial spores, and a much longer soak for a sterilisation claim, where the product has one. Glutaraldehyde solutions are often called by the brand name Cidex in Malaysian clinics, but several brands and chemistries are on the market.

Chemicals you will see

Contact times and temperatures are product-specific. Use only the time on your product’s label and the device maker’s instructions.
ChemicalTypical usePoints to know
Glutaraldehyde (around 2%)High-level disinfection; sterilisation claim only with a very long soakRespiratory and skin sensitiser; needs ventilation and PPE
Ortho-phthalaldehyde (OPA)High-level disinfection, mainly of endoscopes and probesFaster than glutaraldehyde; stains skin and tissue grey
Peracetic acidAutomated reprocessors and some soaksSporicidal; can be corrosive to some metals
Hydrogen peroxide (stabilised)High-level disinfection and some sterilant productsMaterial compatibility varies by device

Why a soak does not replace steam

  • Contact time: high-level disinfection takes minutes to under an hour, but a sterilisation claim can need many hours — around 10 hours for some glutaraldehyde products.
  • No packaging: items come out wet and unwrapped, so they must be used at once and cannot be stored as sterile.
  • Rinsing: residues must be rinsed off, and rinsing with tap water can re-contaminate a sterilised item. Sterile water is needed for a sterile outcome.
  • Monitoring: there is no routine biological test for each soak. You can test the solution’s minimum effective concentration, but not prove each item was sterilised.
  • Solution life: activity drops with dilution and reuse, so the solution needs daily checks and replacement on schedule.
  • Staff safety: fumes and skin contact need a chemical health risk assessment under the Occupational Safety and Health (Use and Standards of Exposure of Chemicals Hazardous to Health) Regulations 2000, plus ventilation and PPE.

Steam vs chemical immersion

Steam autoclaveChemical immersion
Kills sporesYes, in a validated cycleOnly with a sterilant product used for its full sterilisation time
TimeUsually under an hour, including dryingMinutes for disinfection; hours for a sterilisation claim
Packaging and storageYes, in pouches or wrapsNo — use immediately
MonitoringCycle record, chemical and biological indicatorsConcentration test strips and time logs only
Residues and hazardsNone on the instrumentRinse needed; chemical exposure for staff
Best forHeat-tolerant critical and semi-critical itemsHeat-sensitive semi-critical items

Where chemical high-level disinfection belongs

Under the Spaulding classification, heat-tolerant critical items — anything entering sterile tissue — should be steam sterilised. Chemical high-level disinfection is the accepted route for heat-sensitive semi-critical devices that touch mucous membranes, such as flexible endoscopes and endocavity ultrasound probes. For heat-sensitive critical items, hospitals use low-temperature sterilisers rather than a soak where possible. A tray of instruments sitting in disinfectant all day between patients is not sterilisation.

Read next The Spaulding classificationLow-temperature sterilisersUltrasound probe disinfection (ultrasound.my)

Related guides

Medical Steriliser (Sterilizer) Machines for ClinicsSteam, dry heat, UV, plasma and ethylene oxide sterilisers compared — and how to tell which one your clinic’s instruments require.UV Sterilizer Cabinet vs Autoclave: What Each Can DoUV cabinets are sold as “sterilizers”, but they do not sterilise instruments. Here is how they differ from an autoclave and what to use instead.Plasma and Ethylene Oxide Sterilizers: Low-Temperature OptionsFor heat-sensitive devices that cannot go in an autoclave. How the main low-temperature methods work, what they cannot process, and who really needs one.

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Frequently asked questions

Is cold sterilisation as good as an autoclave?
No. For heat-tolerant instruments, steam is faster, can be packaged and stored, and is monitored with biological indicators. Chemical soaks are for devices that cannot take heat.
How long does glutaraldehyde take to sterilise instruments?
It depends on the product. Some glutaraldehyde products quote around 10 hours for a sterilisation claim and a much shorter time for high-level disinfection. Follow the label exactly.
Can I store instruments after a chemical soak?
No. They come out wet and unwrapped, so they must be rinsed as the label directs and used immediately.
Are alcohol or chlorhexidine soaks a form of sterilisation?
No. They are low- or intermediate-level disinfectants and do not kill bacterial spores. They are not suitable for instruments that enter tissue.

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