In the mid-1800s a few microbiologists recognized that certain chemicals reduced microbes. Ignaz Semmelweis suggested that all doctors wash their hands with chlorine water after dessecting cadavers in the morgue and before assisting in the delivery of babies in the maternity wards. In 1860 Joseph Lister developed procedures using carbolic aced on wounds and instruments and as a spray in the air near operating tables. Both of these scientists were important contributors in the understanding of the use of chemicals to reduce microbes.

The number of chemicals available to kill germs is enormous, probably at least 10,000 with 1000 commonly used in the home and hospitals. Chemicals exist as liquids, gasses, and solids. The liquid forms may be aqueous (water base) or tinctures (alcohol base). The minimum inhibiting concentration (MIC), chemical death time (CDT), and phenol coefficient (PC = dilution that kills microbes after 10 minutes but not after 5 minutes of exposure) are used to rank effectiveness of chemicals. The concentration or strength of a chemical may be expresses as a diluation (example – Amphyl is usually diluted 1:200 that is one part of chemical to 200 parts of water by volume); others may be expressed as parts per million (example – chlorine); and alcohol is often expressed in percent solution (alcohol is added to water by weight or volume to have a value of 50% or 80%, etc.).

Many groups of chemicals are used to reduce or destroy microbes. Important chemical groups include halogens, phenols, soaps and detergents, ammonia compounds, alcohols, heavy metals, acids and bases, allicins, and special compounds like gluteraldehyde. It is estimated that nearly 30% of all currently used antimicrobial chemicals have halogens as the active ingredient. Bromine, chlorine, and iodine are three commonly used halogens. Because bromine is more dangerous to handle, chlorine and iodine are frequently used in disinfectants and antiseptics. Halogens kill vegetative bacteria, viruses, and fungi; but the effectiveness against endospores continues to vary with each research experiment. Common household bleach (5% sodium hypochlorite), chloramines, and betadine are only three of the various halogen compounds used to disinfect equipment, sanitize skin surfaces, and reduce microbes in water. Halogens disrupt the cellular activities and are effective antimicrobial chemicals, so 10% bleach will effectively reduce microbes on tools used to trim bushes and other plants and iodine based teat dips reduce the spread of microbes in dairy cows. However, the activity of halogens is greatly reduced by the presence of organic matter and alkaline pH; and halogens have toxic effects on dialysis patients and fish gills.

The toxic and antimicrobial powers of the phenols has been studied since their first use buy Joseph Lister. Phenols apparently disrupt cell walls, cell membranes, and important protein activities in cells. Many phenols have been determined to be too toxic to use antiseptics, even though the phenols like hexachlorophene have been sold in soaps for use in burn units and nurseries. Presently, these phenols are being replaced with other chemicals that are not as easily absorbed through the skin and possible causing nerve damage. Phenols are known to effectively reduce Streptococcus and Staphylococcus so compounds like Amphyl and O-syl are still used for hospital and laboratory disinfection.

Soaps, detergents, and ammonium compounds (quats) are commonly used to control microbes. Many detergents can be diluted 1:100 or 1:1000 and used to disinfect and clean walls, furniture, and public restrooms. Soaps are weak anti-microbial chemicals and destroy only very sensitive microbes. The sudsing effect of soaps helps to remove large amounts of microbe-containing debris. Alcohol added to soap (green soap) makes it more germicidal; and washing hands with soap for 15 minutes does effectively remove resident microbes on the skin. Soap will never sterilize skin; and some pathogenic microbes like Pseudomonas mayeven grow in soap dishes. We therefore recommend liquid soap dispensers in all health-care facilities.

Alcohols and peroxides are anti-microbial. Rubbing alcohol (isopropyl) and 3% hydrogen peroxide have been used for skin and wound cleaning. The possible toxic effects of these chemicals, as well as the potential damage done by betadine, require that we use these chemicals very carefully on skin wounds. Using alcohols and peroxides is still approved for the destruction of bacteria, fungi, and viruses.

Chemicals with high atomic weights are called heavy metals. Health and environmental considerations have greatly reduced the use of heavy metals. Compounds containing copper, silver, and mercury should not be used on broken skin because they delay healing. Mercurochrome is now considered a poor antiseptic; and silver nitrate, which was commonly used to prevent gonococcal infections in the eyes of newborn infants, is not used because of its toxic effects and failure to inhibit or kill Chlamydia. Copper sulfate may be used as an algicide in home aquaria and as a fungicide (Bordeaux mixture) to reduce fungal growth in grape vineyards and golf course greens.

Acids and bases are usually too caustic to use as microbial controls. Some oganic acids are widely used as food preservatives to prevent microbial growth. Phosphoric acid also dissolves milkstone in dairy operation pipelines – thus removing the possible homes for microbes. Also allicins (natural extracts from plants like garlic) have been the center of discussion for centuries. Consuming garlic has been thought to increase courage, absorb air pollutants, bind-up heavy metals and allow them to pass in feces, cure respiratory diseases and meningitis, possess aphrodesiac powers, help reduce parasites, and improve healing when applied to wounds. Laboratory studies seem to confirm that extracts from garlic do inhibit the growth of some bacteria including E.coli.

One of the presently accepted chemicals used as a sterilant and disinfectant is gluteraldehyde. It kills endospores in 3 hours and bacteria and viruses in a few minutes. It is less corrosive than most chemicals, not inhibited by organic matter like blood, and does not damage plastics. Similarly to gluteraldehyde, the gas ethylene oxide (ETO) is accepted for use as a killer of microbes. Sterilization with ETO requires up to three hours, is potentially explosive, and sterilized items must be aerated for several hours to protect workers from mucous membrane damage and possible carcinogenic effects.