How to choose a disinfectant

How to choose a disinfectant

How to choose a disinfectant

Article by KR Snyman (BPharm, MSc Pharmaceutics) JR Snyman (MBChB, MPharmMed, MD)

Step one:

First look at the tests done and accreditation status of the product i.e. SABS or similar registration as this confirms the validity of claims about the antimicrobial activity. The product must submit proof of efficacy to obtain this accreditation.

Step two:

Don’t be fixated on the concentrations of the various ingredients as this means little if not understood and evaluated in context of the product’s intended use e.g. hand sanitisers often contain additional products to prevent excessive drying of the skin while others need to be less corrosive to the surface they must be used on. All these properties are taken into consideration when products get their registration for use.

Step three:  

Use a product for its labelled use indication as that will guarantee successful protection.

Step four: 

Select products which are non-irritating and does not trigger allergies or eczema if you are prone to be sensitive to colourants and fragrances. Use protective gloves when scrubbing and disinfecting surfaces with e.g. oxidizing or agents with similar activity.

Why do we need disinfectants?

The spread of the common cold, influenza and many other infectious diseases may be prevented by using the correct disinfectants on surfaces as well as in hand sanitation on a regular basis.5,6  This prevents the spread of viruses and even organisms causing TB and other infectious diseases from person to object to person.

A disinfectant is defined as a chemical substance which has the ability to destroy harmful micro-organisms, such as bacteria, viruses, moulds, mildews and fungi, especially on non-living objects as well as provide effective protection when used as hand sanitation devices.1  Disinfectants are required to be effective and safe regardless of any other compounds present during use.  They must also be stable in both diluted and concentrated forms.2-6

Disinfectants are often graded according to their effectivity against the microbes compared to phenol.7 Another measure to determine disinfectant effectiveness is the United States Environmental Protection Agency (EPA) classification scale as either high, intermediate or low levels of disinfection.  High level disinfection refers to the disinfectant killing all organisms, except high levels of bacterial spores.  The intermediate level disinfectants are classified by their ability to kill mycobacteria (group of bacteria which includes the causative agents of leprosy and TB), most viruses as well as bacteria.  Finally, low level disinfectants are classified as agents which kill some viruses and bacteria.8 

A good disinfectant is characterised according to the following factors:

  1. Broad spectrum against germs, spores and fungi
  2. Slight to moderate efficiency in the presence of organic matter
  3. Slight residual activity
  4. Must be both active as well as stable
  5. Safe for humans and animals, moderate toxicity
  6. Environmentally safe
  7. Leaves no damage or odour
  8. Non-corrosive
  9. Affordable
  10. Straightforward usage.2,3

Commonly used disinfectant categories include: Alcohols, Alkalis, Aldehydes, Oxidising agents (Chlorine bleaches), Phenols and quaternary Ammonium products. These products are often combined for specific reasons to improve activity or application properties.


Alcohols, between 60-90 %, are considered to be good general disinfectants. However, the usefulness of alcohol as a single agent decreases as the concentration used is below 50 %. It is important to understand that higher concentrations of alcohol within a disinfectant do not necessarily generate more desirable effects against bacteria, viruses and fungi. Noteworthy is that one gets various types of alcohols and those most often used are ethanol (fermented from plant products e.g. sugar cane etc) and those such as propylene (from natural gas) based origin e.g. isopropyl alcohol (isopropanol).

These are fast acting disinfectants with rapid evaporation time which leave no residue.  Alcohols may have a strong smell and can harden certain rubbers and plastics.  Alcohols are active against bacteria, fungi, and tuberculosis (TB) causing organisms.  However, alcohols have limited activity against viruses and have no activity against spores.  Solutions with an isopropyl alcohol concentration above 91 % can kill bacteria but may require longer contact time for disinfection and thus allow spores to lie dormant without being killed.  Alcohols are also highly flammable.4 


Calcium hydroxide, sodium carbonate and calcium oxide are only a few of the disinfectants which form part of the alkali group.  Alkalis have a slower acting disinfecting time which are affected by pH and perform optimally at higher temperatures.  These agents are corrosive to metals and may cause severe skin burns as well as mucous membrane irritation.  Alkalis are active against bacteria, viruses, fungi as well as spores.  Alkalis show limited action against pathogens causing TB.4


This class of disinfectants includes agents such as glutaraldehyde. These disinfectants have gained wide acceptance as high-level disinfectants as well as a chemical sterilant.  It is a slow acting disinfectant which is affected by both pH as well as temperature.  It is a colourless liquid with a pungent smell and is classified as non-corrosive.  Glutaraldehyde is proven to be able to kill bacteria, viruses, fungi, and TB causing organisms as well as spores.4 A 2% solution of glutaraldehyde exhibits good activity against vegetative bacteria, spores as well as viruses.  Glutaraldehyde is 10-fold more effective than formaldehyde and is less toxic. Patents enhancing the penetration of glutaraldehyde into the fatty outer layers of micro-organisms e.g. combining with surfactants enhances the potency of the product.

Oxidising Agents: (Halogens: Chlorine & Iodine; Peroxygen Compounds)

Halogen disinfectants containing chlorine such as sodium hypochlorite (bleach), calcium hypochlorite and chlorine dioxide are fast acting agents which are affected by pH and require frequent application and are inactivated by UV radiation.  These agents can corrode metals, rubbers as well as fabrics.  Chlorine halogens cause mucous membrane irritation and may release a toxic gas if mixed with strong acids or ammonia.  Chlorine disinfectants are active against bacteria, viruses, fungi, TB causing organisms as well as spores.4


Phenol disinfectants may leave a residual film on treated surfaces and can damage rubber and plastic but are non-corrosive.  Phenols are stable in storage but may cause irritation to skin as well as to eyes.  Phenols are considered toxic to animals especially to cats and pigs.  Phenols are effective against bacteria, fungi, viruses, as well as TB causing organisms but have no effectivity against spores.4

Quaternary Ammonium Compounds

Benzalkonium chloride are stable in storage and provide best activity at neutral or alkaline pH.  Quaternary Ammonium Compounds are effective at high temperatures.  Higher concentrations are corrosive to metals and cause irritation to skin, eyes and the respiratory tract.  Quaternary Ammonium Compounds are effective against bacteria, selective viruses, fungi and spores.  These agents show no activity against TB causing organisms pathogens.4

Combination products

In many cases the combination of two or more different disinfectants poses beneficial in the sterilization of surfaces and or when used to sterilise medical equipment as well as in skin sanitation products. However, disinfectants cannot merely be mixed or used in combination without the proper knowledge of each mechanism of action as different disinfectants may either enhance the action of the other or cause reactions which in turn delay or stop disinfection completely.12

Soap versus disinfectant

Cleaning with water and the use of soap is referred to as the physical removal of dirt and grease and in process some of the pathogens which may cause disease.  When cleaning with the use of soap one simply moves pathogens from one surface to another.  Disinfection allows for the elimination of pathogens from these surfaces as well as rendering these pathogens incapable of reproduction.13 Proper hand washing also removes other organic or non-organic material which may impair the efficacy of the disinfectant being used e.g. the disinfectant binds to the other material meaning that for a better effect hands should be clean before a disinfectant is used and then select a disinfectant which is more friendly to your skin and remember to use a good moisturiser to prevent cracks and other hiding places for germs.


  1. Dictionary, Merriam-Webster, Accessed 11 Apr. 2020.
  2. Characteristics of a good disinfectant. 2017. Safespace®. Accessed 11 Apr. 2020.
  3. General characteristics of disinfectants. Mississippi state university Extension. Accessed 11 Apr. 2020.
  4. Characteristics of selected disinfectants. 2018. The centre for food security & public health. Iowa State University.
  5. Science Clarified. “We Are Surrounded.” Accessed 1 Apr 2020
  6. Rutala, William A. “Selection of the Ideal Disinfectant.” Accessed 11 Apr 2020.
  7. Sandle T, ed. 2012. The CDC Handbook: A Guide to Cleaning and Disinfecting Cleanrooms (1st ed.). Grosvenor House Publishing Limited.
  8. Centers for Disease Control and Prevention (21 December 2012). “Sterilization or Disinfection of Medical Devices”. CDC. Archived.
  9. Vijayakumar R, Kannan VV, Sandle T, Manoharan C (May 2012). “In vitro Antifungal Efficacy of Biguanides and Quaternary Ammonium Compounds against Cleanroom Fungal Isolates”. PDA J Pharm Sci Technol.66(3): 236–42
  10. Disinfectants and sterilization methods.   Environmental health and safety. University of Colorado Boulder. Accessed 12 Apr 2020.
  11. Patnayak, D.P., Prasad, M., Malik, Y.S., Ramakrishnan, M.A. & Goyal, S.M. 2007. Efficacy of disinfectants and hand sanitizers against avian respiratory viruses. Avian diseases, 52:199-202.
  12. Figueroa, A., Hauck, R., Saldias-Rodriguez, J. & Gallardo, R.A. 2017. Combination of quaternary ammonia and glutaraldehyde as a disinfectant against enveloped and non-enveloped viruses. Poultry science association Inc. p1-7.
  13. Rose, J.B. 2013. Cleaning vs. disinfecting: what’s the difference?. Water quality & Health council.