4.3.2 Classification and use of skin disinfectants
1.Common skin disinfectants
Disinfectants are classified by mechanisms，effect，objects，etc.According to the mechanisms，they can be ambiguously classified into chemical disinfectants and biological disinfectants（e.g.，enzymes and bacteriophages）.Of which，chemical disinfectants are the most widely used and most diverse disinfectants which can be further classified into oxidized and non-oxidized disinfectants according to the types of chemical reaction.Oxidized disinfectants mainly include halogens（e.g.，chlorine，bromine，and iodine）and peroxides（e.g.，hydrogen peroxide，peroxyacetic acid，and chlorine dioxide）；non-oxidized disinfectants mainly include alcohols（e.g.，ethanol），phenols（e.g.，para-chlorometa xylenol），quaternary ammonium salts（e.g.，benzalkonium chloride），guanidines（e.g.，polyhexamethylene biguanide hydrochloride，chlorhexidine），aldehydes（e.g.，glutaraldehyde）and metals（e.g.，silver）.
According to the ability of killing microorganisms，disinfectants can be classified into high-efficiency，medium-efficiency and low-efficiency.It is believed that high-efficiency disinfectants，which in general contain chlorine，peroxides，or aldehydes，can kill all microorganisms including bacterial spores，fungal spores，and viruses.Medium-efficiency disinfectants which in general contain iodine or alcohol，can not kill bacterial spores.Lowefficiency disinfectants（e.g.，certain guanidines and certain quaternary ammonium salts），can only kill general bacterial propagules，some fungi and lipophilic viruses，without ability of killing Mycobacterium tuberculosis，hydrophilic viruses and bacterial spores.
Common categories of skin disinfectants include iodine，alcohols，phenols，peroxides，guanidines，and quaternary ammonium salts，etc.
（1）Iodine-containing disinfectants：Iodine is a widely used ingredient of skin disinfectants.Iodine molecules can quickly penetrate the cell wall to combine with amino acids and unsaturated fatty acids，resulting in difficulty in protein synthesis and changes in cell membranes.The iodine-containing disinfectants commonly used in clinical practice are iodine tincture（e.g.，iodine wine），iodophor and povidone-iodine solution.Povidone iodine，an amorphous complex formed by the combination of iodine and surfactant，is currently the most important iodine-containing skin disinfectant，as well as mucous membrane disinfectant.The surface active ingredients contained in it can change the wettability of the solution to the object and form an extremely thin sterilization film on the skin surface which is able to assist iodine to penetrate organics，emulsify fat，release effective iodine slowly and permanently to strengthen the sterilization ability of iodine.
（2）Alcohol-containing disinfectants：Ethanol belongs to the medium-efficiency disinfectants，with an optimal effective concentration of 75％to 85％.Soaking or wiping with 60％to 90％ethanol aqueous solution can kill bacterial propagules，mycobacteria，yeasts，fungi and some viruses，except bacterial spores.The dehydration of ethanol can make the bacterial protein coagulate and denature，and its penetration can make it penetrate the cell wall and enter the bacterial body to play the disinfecting role.Although ethanol can quickly kill bacterial propagules，it is not lasting.In addition，it is volatile and irritating，which can not be applied to mucosa or large wounds.The combination of ethanol and other chemical antibacterial agents produces a synergistic antibacterial effect.For example，the compounding of multiple alcohol solutions can shorten the effective action time and improve the sterilization ability，especially to virus.
Isopropyl alcohol belongs to the medium-efficiency disinfectants as well，with similar sterilization mechanism to that of ethanol.Isopropyl alcohol has a slightly stronger sterilizing ability and toxicity than ethanol.Currently，ethanol is extensively used in China，while isopropyl alcohol is widely used abroad.Isopropyl alcohol can completely kill lipid viruses，but it has no inactivating effect on non-lipid enteroviruses.Its commonly-used concentration is 70％-80％，and 70％isopropanol can kill hepatitis B virus，hepatitis C virus and human immunodeficiency virus within 10 min.
（3）Phenol-containing disinfectants：Trichloro hydroxyl diphenyl ether，a broadspectrum，high-efficiency antibacterial agent，also known as triclosan，is an important phenol-containing disinfectant.Its effective antibacterial concentration is 0.2％-2.0％.Triclosan penetrates into the bacterial cell and affects the cell plasma membrane and synthesis of RNA，fatty acid and protein.Triclosan has a certain degree of antibacterial effect，but tends to show more bacteriostatic effect.In addition，it has a stronger effect on Gram-positive bacteria（including MRSA）than Gram-negative bacteria，especially Pseudomonas aeruginosa and a certain activity against Mycobacterium and Candida，but has a weak activity against filamentous fungi.Studies have shown that triclosan is mildly teratogenic.(https://www.daowen.com)
（4）Peroxide-containing disinfectants：Peroxide-containing disinfectants mainly include hydrogen peroxide and peracetic acid，and can kill all microorganisms such as bacteria，fungi，spores and viruses.Of which，peracetic acid has the strongest sterilization ability，followed by hydrogen peroxide.Peroxide-containing disinfectants are high-efficiency，quickacting，and low-toxic disinfectants，which need to be used and prepared instantly.At high concentrations，they can irritate and damage skin and mucous membranes.The concentration of hydrogen peroxide solution up to 1000 mg/L has a bactericidal effect.Clinically，hydrogen peroxide solution is often used to gargle and clean wounds in patients with oral inflammation.The concentration of peroxyacetic acid solution should be less than 2000 mg/L when it is used for skin disinfection，and be reduced to 200 mg/L when it is used for mucosa disinfection.
（5）Guanidine-containing disinfectants：Chlorhexidine，a low-efficiency disinfectant，also known as chlorhexidine，is a biguanide antibacterial agent with low toxicity，low irritation，and broad antibacterial spectrum.The chlorhexidine is easily adsorbed on the bacterial body to damage the cell membrane and inhibit the action of bacterial system enzymes to hinder the bacterial metabolism，through which it is mainly used as an antibacterial treatment for skin and mucous membranes.Moreover，high concentration of chlorhexidine can make the cell cytoplasm aggregated，concentrated and denatured to achieve the purpose of sterilization.Chlorhexidine can effectively kill bacterial propagules，but has only an inhibitory effect on spores，tuberculosis and fungi，and a weak ability to kill hepatitis B and C viruses and fungal strains of Aspergillus niger.
（6）Quaternary ammonium salt-containing disinfectants：Quaternary ammonium saltcontaining disinfectants are low-efficiency disinfectants，including single-chain quaternary ammonium salts and double-chain quaternary ammonium salts，such as dodecyl dimethylbenzyl ammonium bromide（e.g.，benzalkonium bromide），dodecyl dimethylphenoxyethyl ammonium bromide（e.g.，domiphen）and myristyl dimethylpyridine ammonium bromide.It can adsorb on the surface of the bacteria to change the permeability of the bacteria，along with leakage of intracellular substances and denaturation of proteins，consequently obstructing the process of cell metabolism to achieve the effect of sterilization.The disinfectants have the characteristics of low bactericidal concentration，good water solubility，low toxicity，low irritation，stable properties，etc.，but the price is comparatively expensive，the effect of killing certain viruses is poor，and there are many compatibility taboos.The presentative product，benzalkonium bromide，has a strong antibacterial effect，but it cannot kill fungi，Mycobacterium tuberculosis，bacterial spores，and non-cladding viruses.The clinically used concentration of benzalkonium bromide is 1000 mg/L，which can be used to clean the skin of patients，and clean the hands of medical staff，etc.It is usually used in the combination with alcohol disinfectants.
2.Disinfection procedures and attention points
（1）Thorough cleaning is the prerequisite to ensure the disinfection effect.Prior to skin disinfection，the skin should be cleaned specifically in accordance with the pollution types of the skin.Incomplete cleaning or decontamination will affect the disinfection effect.
（2）Correctly select the type and concentration of disinfectant.Take ethanol as an example，it has the best disinfection effect at a concentration of 70％-80％.
（3）Sufficient action time is required.The action time of different skin disinfectants varies.Generally，it takes 1-5 min or is subjected to thorough natural drying to reach the disinfection standard.