Clinical guides
What is sterilization? Sterilization vs disinfection and the main methods
What is sterilization, how it differs from disinfection and sanitization, and how steam, dry heat, ethylene oxide, peroxide and radiation methods compare.
Sterilization is a validated process that destroys all forms of microbial life on an object, including bacterial spores. In health care, what is sterilization versus disinfection comes down to that difference: disinfection kills most pathogens but not necessarily spores. Which one a device needs depends on how it touches the patient, and the method depends on what the device can tolerate.
What is sterilization?
Sterilization is an absolute target managed statistically. Because microbial death follows a logarithmic curve, no process can prove that every single organism is dead. Instead, a validated sterilization process is designed to reach a sterility assurance level (SAL) of 10^-6, meaning no more than a one-in-a-million chance that a single viable microorganism survives on an item.
Sterilization is achieved by heat (moist or dry), chemicals (gases or liquids) or radiation. International standards describe how each process is developed, validated and routinely controlled, for example:
- ISO 17665 for moist heat (steam)
- ISO 20857 for dry heat
- ISO 11135 for ethylene oxide
- ISO 11137 for radiation
- ISO 22441 for low-temperature vaporized hydrogen peroxide
A medical sterilization definition used in practice therefore always has three parts: a cleaned item, a validated process and documented proof that the process ran correctly.
Sterilization vs disinfection vs sanitization
The three terms describe very different levels of microbial kill and are not interchangeable.
| Term | What it does | Kills spores? | Typical use |
|---|---|---|---|
| Sterilization | Destroys all microbial life to SAL 10^-6 | Yes | Surgical instruments, implants, items entering sterile tissue |
| High-level disinfection | Kills all vegetative bacteria, viruses, fungi and mycobacteria; some spores | Not reliably | Semi-critical devices such as many flexible endoscopes |
| Intermediate- and low-level disinfection | Kills most vegetative bacteria and many viruses | No | Blood pressure cuffs, bed rails, exam tables, floors |
| Sanitization | Reduces microbes to levels judged safe by public health standards | No | Food-contact surfaces, general cleaning |
| Cleaning | Physically removes soil and many microbes | No | Required before every disinfection or sterilization step |
The difference between sterilizing and disinfecting matters most for reprocessed instruments: a disinfected surgical instrument is not safe for surgery, even if it looks clean.
Some everyday examples make the distinction concrete:
- Sterilization examples: a wrapped set of surgical instruments processed in a steam sterilizer, single-use syringes irradiated at the factory, a catheter sterilized with ethylene oxide, culture media autoclaved in a laboratory.
- Disinfection examples: a flexible endoscope reprocessed in an automated endoscope reprocessor with a high-level disinfectant, a bedside table wiped with a hospital-grade disinfectant between patients.
- Sanitization examples: kitchen counters and food-contact surfaces in a hospital catering area.
Antisepsis is a separate term again: it means reducing microorganisms on living skin or mucous membranes, for example before an injection or incision.
The Spaulding classification: which items need sterilization?
Most infection-prevention programs decide between sterilization and disinfection with the Spaulding classification, which sorts devices by infection risk.
- Critical items enter sterile tissue or the vascular system: surgical instruments, implants, needles, biopsy forceps. They must be sterile.
- Semi-critical items contact mucous membranes or non-intact skin: many endoscopes, laryngoscope blades, some probes. They need at least high-level disinfection, and sterilization when the device allows it.
- Non-critical items touch only intact skin: stethoscopes, bed frames, blood pressure cuffs, examination tables. Low- or intermediate-level disinfection is enough.
Always follow the device manufacturer's instructions for use (IFU) and your facility's infection-prevention policy, which may be stricter than the basic classification.
Steam (moist heat) sterilization
Moist heat sterilization uses saturated steam under pressure. It is the first-choice method for anything that tolerates heat and moisture, because it is fast, leaves no toxic residue and costs little per cycle.
Typical sterilization temperatures are 121°C (250°F) and 134°C (273°F). At 134°C a vacuum-type sterilizer holds the load for about 3 to 4 minutes; at 121°C holding times are longer, commonly 15 to 30 minutes depending on load and air removal. The full steam sterilization process includes air removal, heating, exposure, exhaust and drying.
Hospitals run steam sterilization in benchtop units such as the 18–23 L KL-ST001 Portable Pressure Steam Sterilizer and large horizontal chambers such as the KL-ST004 Horizontal Pressure Steam Sterilizer. Our autoclave and steam sterilizer guide explains classes, cycles and sizing.
Dry heat sterilization
Dry heat sterilization uses hot air without moisture. Because air carries heat much less efficiently than condensing steam, it needs higher temperatures and longer times. Common dry heat sterilization temperatures are:
- 160°C (320°F) for 120 minutes
- 170°C (340°F) for 60 minutes
Exposure time is counted after the whole load reaches temperature. Dry heat suits glassware, metal instruments that steam would corrode, powders and oils that steam cannot penetrate. It is unsuitable for plastics, rubber and textiles.
A general laboratory drying oven is not automatically a dry heat sterilizer. For example, Keling's KL-DT001 Electrothermal Constant-Temperature Drying Oven drying oven (40–136 L, up to 250°C) is designed for drying and heating glassware and samples; if you intend to sterilize in an oven, the process must be validated to ISO 20857 for your loads.
Ethylene oxide (EO or EtO) sterilization
Ethylene oxide sterilization is a low-temperature gas method used for heat- and moisture-sensitive devices, and it is widely used for single-use medical devices sold sterile. EO kills microorganisms by alkylating their proteins and DNA, and it penetrates packaging and long lumens very well.
The ethylene oxide sterilization process has four phases: preconditioning and humidification, gas introduction, exposure, and evacuation followed by aeration. Typical operating ranges are a gas concentration of about 450–1,200 mg/L, a temperature of about 37–63°C, relative humidity of 40–80% and an exposure time of 1 to 6 hours. Aeration then takes many hours, often 8 to 12 hours at 50–60°C in a heated aerator, to bring residues below the ISO 10993-7 limits.
The trade-offs are significant. EO is toxic, flammable and a human carcinogen, so an EO gas sterilizer needs a dedicated room, ventilation, emission control, continuous monitoring and trained staff. Total turnaround is long. For these reasons many hospitals send EO work to contract sterilization providers or use hydrogen peroxide systems for heat-sensitive instruments.
Low-temperature hydrogen peroxide and other chemical sterilization
Chemical sterilization covers several low-temperature processes:
- Vaporized hydrogen peroxide and hydrogen peroxide gas plasma: short cycles at low temperature, no toxic residue (by-products are water and oxygen). Limits apply to cellulose materials, liquids and long or narrow lumens, so check device compatibility claims.
- Low-temperature steam and formaldehyde (LTSF): used in some countries for heat-sensitive devices.
- Liquid chemical sterilants such as peracetic acid systems or high concentrations of glutaraldehyde with long contact times: items are processed unwrapped and used promptly, so they cannot be stored sterile.
Radiation sterilization
Radiation sterilization uses gamma rays, electron beams or X-rays to break microbial DNA. It is an industrial method for single-use products such as syringes, gloves, sutures and implants, not something a hospital runs on site. Doses are validated per product under ISO 11137; 25 kGy is a widely used reference dose. Radiation leaves no residue and works through sealed final packaging, which makes it ideal for terminal sterilization at the factory.
Comparing the main sterilization methods
| Method | Typical conditions | Best for | Main limitations |
|---|---|---|---|
| Steam | 121°C or 134°C, minutes | Metal instruments, textiles, heat-tolerant devices | Heat- and moisture-sensitive items |
| Dry heat | 160–170°C, 1–2 h | Glassware, powders, oils | Slow; damages plastics and rubber |
| Ethylene oxide | 37–63°C, hours plus aeration | Heat-sensitive devices, long lumens | Toxic gas, long cycle, emission control |
| Hydrogen peroxide | Low temperature, short cycle | Heat-sensitive reusable instruments | Material and lumen limits |
| Radiation | Validated dose, e.g. 25 kGy | Industrial single-use products | Industrial plant; some polymers degrade |
Before sterilization: cleaning and packaging
No sterilization process can compensate for poor preparation. Organic soil and biofilm shield microorganisms from steam and gas, so items must be cleaned, rinsed, dried and inspected first, then packaged in a system compatible with the method, such as wraps or pouches to ISO 11607 or perforated stainless steel trays like the KL-TC076 Stainless Steel Sterilization Tray inside a wrap or rigid container.
Process verification follows each cycle: physical readouts, chemical indicators and biological indicators, explained in our sterilization indicators guide. The full workflow is in our sterile processing department guide.
This article is educational and intended for trained staff. Always follow local regulations, your infection-prevention protocols and each device's IFU.
Next steps
Map your reusable devices to the Spaulding categories, confirm which methods each device's IFU allows, and size steam capacity first, since it covers most loads. Browse Keling's laboratory and sterilization equipment and request a quote when you are ready to equip a clinic, laboratory or sterile processing area.
Frequently asked questions
What is sterilization in simple terms?
Sterilization is a validated process that kills or removes every form of microbial life on an object, including resistant bacterial spores. In health care it is applied to instruments that enter sterile tissue or the bloodstream, such as surgical instruments and implants. The result is defined statistically, usually as no more than one chance in a million of a surviving microorganism.
What is the difference between sterilizing and disinfecting?
Sterilizing kills all microorganisms, including spores. Disinfecting kills most disease-causing microorganisms on objects or surfaces but may leave some spores alive. High-level disinfection comes close to sterilization and is accepted for semi-critical devices such as many flexible endoscopes, while surgical instruments that enter sterile tissue must be sterilized.
Is ethylene oxide sterilization safe?
Ethylene oxide sterilization is safe for patients when the product is properly aerated so residues fall below the limits in ISO 10993-7. The gas itself is toxic, flammable and classified as a human carcinogen, so EO sterilizers need dedicated ventilation, emission controls, gas monitoring and trained operators. Many hospitals now outsource EO processing or use other low-temperature methods.
What temperature is used for dry heat sterilization?
Common dry heat sterilization settings are 160°C (320°F) for 2 hours or 170°C (340°F) for 1 hour of exposure, counted after the load reaches temperature. Dry heat is much slower than steam because hot air transfers heat poorly. It suits glassware, powders, oils and metal items that steam would corrode or cannot penetrate.
What two things need to be completed prior to sterilization?
Items must be thoroughly cleaned and then correctly prepared, which means inspected, dried, assembled and packaged in a material compatible with the sterilization method. Cleaning removes the soil and biofilm that protect microbes, and correct packaging lets the sterilant reach every surface while keeping the item sterile afterward until it is opened.
Which sterilization method is used most in hospitals?
Steam sterilization is the most widely used method in hospitals because it is fast, reliable, non-toxic and inexpensive per cycle. Hospitals keep low-temperature methods such as hydrogen peroxide gas or ethylene oxide for devices that cannot tolerate heat or moisture, such as some flexible scopes, cameras and powered instruments.
Can you sterilize with alcohol or bleach?
No. Alcohol and household-strength chlorine solutions are disinfectants, not sterilants: they do not reliably kill bacterial spores within practical contact times. They are useful for skin antisepsis or surface disinfection. Liquid chemical sterilization requires a sterilant registered or approved for that claim, used at the stated concentration, temperature and contact time.
