Sterilization: what types and their importance in health

The cleaning and sterilization process involves not only removing dirt, but also the total elimination of all microorganisms present in instruments, clothing, equipment, products and medical – laboratory tools for use in patient care. This practice has been adopted since the 9th century BC, when Homer pointed out the use of sulfur as a disinfectant. Since then, this process has been used to ensure the health and safety of healthcare professionals and patients.


Sterilization is a process that aims to destroy all microbial life forms that can contaminate health-related products, materials and objects. Therefore, organisms such as viruses , bacteria and fungi are eliminated during sterilization .

We say that the sterilization process was effective when the probability of survival of the microorganisms is less than 1: 1,000,000.

In addition, sterilization ensures:

  • Safety for patients and professionals
  • Compliance with legal rules established by Anvisa
  • Longer life of medical materials
  • Resource savings and optimization
  • The disinfection process, despite being effective for eliminating microorganisms, does not destroy spores and some types of viruses. Thus, just disinfecting is not enough.

Understanding materials treatment processes

In addition to the type of material, it is necessary to classify it according to its direct or indirect use in the patient, which will result in three categories: critical, semi-critical and non-critical. This will determine the form of processing to which it will be subjected: cleaning, disinfection or sterilization. Namely, critical materials are those that come into contact with bloody tissues, semi-critical materials are those that come into contact with mucous membranes and non-critical materials only come into contact with intact skin. In general, during the treatment processes, critical materials must be sterilized or single-use (disposable), semi-critical materials must be sterilized, or at least disinfected, and non-critical materials must be disinfected, or at least , clean.


There are several ways to perform sterilization. However, the decision of which process to use must be based on the type of material and the risk of contamination.

Sterilization methods can be divided into chemical (phenolic compounds, chlorhexidine, halogens, alcohols, peroxides, ethylene oxide, formaldehyde, glutaraldehyde and peracetic acid) and physical (heat, filtration and radiation). In order to choose the best method, in addition to material compatibility, effectiveness, toxicity, ease of use, costs, among others, must be taken into account.

Chemical sterilization methods

It is indicated for critical and thermosensitive articles, that is, those that cannot resist the high temperatures of physical processes.

Among the chemical methods, some of them can be used both to disinfect and to sterilize, it depends only on the time of exposure and concentration of the agent. The most used for laboratory and hospital products are:

  • Ethylene oxideETO ): it is a gas widely used in the sterilization of laboratory and hospital materials for single use because of its good cost / benefit. Its action occurs through the reaction with a protein in the cell nucleus, preventing reproduction. All products must be placed in gas-permeable packaging to allow ETO to penetrate. Its use does not damage the materials and can be used in several types of materials, including thermosensitive materials. However, it is highly toxic and aggressive to the external environment.
  • Peracetic Acid: it has fast action, low toxicity and is biodegradable. However, it damages metals. A great advantage is being effective even in the presence of organic matter (that is, the materials do not need to be cleaned beforehand). In return, the materials must be used immediately after sterilization by this method, so it is not used much.
  • Hydrogen peroxidehydrogen peroxide): in a concentration of 3% and 6% it has fast action, it is biodegradable and non-toxic, but it has a high corrosive action. Its action is more effective in hemodialysis capillaries and contact lenses, but this process is not widely used.
  • Formaldehyde: can be used in gaseous and liquid form and, to have sporicidal action, requires a long exposure time. It is indicated for catheters, drains and tubes, laparoscopes, arthroscopes and ventriloscopes, acrylic grafts. Because it is carcinogenic and irritating to mucous membranes, its use is more restricted.
  • Glutaraldehyde: liquid with a powerful biocidal action and can be used in thermosensitive materials, but it needs a long exposure time to be sporicidal. It is widely used due to its low cost and low corrosive power, but it is irritating to the airways; it can cause burns on the skin, membrane and mucous membranes; and porous materials can retain the product. Acrylic grafts, catheters, drains and polystyrene tubes are the materials routinely sterilized by this process.

Physical sterilization methods

Sterilization by physical processes can be through moist heat, dry heat or radiation. Radiation sterilization has been used on an industrial level for medical and hospital articles. It allows low temperature sterilization, but it is a costly method. For materials that resist high temperatures, heat sterilization is the method of choice, as it does not form toxic products, it is safe and low cost.

  • Ionizing radiation: it destroys DNA forming super-reactive radicals (superoxides), killing or inactivating microorganisms (when they are unable to reproduce). Many materials are compatible with this type of sterilization, as there is no increase in temperature in this process. Case of thermosensitive materials and biological tissues for transplants. Although it appears, radiation is not transmitted to processed products. It is a waste-free and ecological process, as it does not generate toxic emissions or residues, in addition to not impacting air or water quality. We will highlight two types of them:
  • Gamma Radiation: the energy is generated by Cobalt 60 sources. This process has a high penetrating power, allowing the products to be sterilized in the final packaging, without the need for manipulation.
  • E-beam(electron beam): used preferably for the processing of high-volume / low-density products, such as medical syringes, or low-volume / high-value products, such as cardiothoracic devices. In addition, it can be used for biological products and fabrics. They can be sterilized in the final packaging, since E-beam radiation also has a high penetrating power. The great advantage of this type of radio-sterilization is that it requires less exposure time, avoiding disruptions and long-term aging effects that can happen with polypropylene when subjected to prolonged radiation
  • Moist heat(eg, autoclaving, boiling and pasteurization): causes denaturation and coagulation of proteins and fluidization of lipids. It cannot be used in thermosensitive materials, nor for materials that oxidize with water. Autoclaving is widely used in various sectors of health services because it is affordable and easy to use. In addition, it manages to sterilize a multitude of materials, including fabrics and solutions.
  • Dry heat(eg stove, buckling and incineration): causes oxidation of organic cell constituents. It penetrates into substances more slowly than wet heat and therefore requires higher temperatures and longer times. It cannot be used for thermosensitive materials.
  • Filtration: used for solutions and thermolabile gases, when they pass through filter surfaces with very small pores, such as porous candles, asbestos discs, porous glass, cellulose filters, and “millipore” filters (cellulose acetate or polycarbonate membranes).
  • Non-ionizing radiation(eg, UV light): alters DNA replication at the time of reproduction. Widely used in germicidal lamps found in operating rooms, wards, nurseries, laminar flow hoods. Its disadvantages are: low penetrating power and deleterious effects on the skin and eyes, causing severe burns.


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