Surface-tension depressants used essentially for cleansing surfaces are generally known as detergents. Two examples of these are soaps and surfactants. Of course, soaps are all too common cleansing agents that everyone is familiar with. This can’t be said though of surfactants, although these are extensively used in many of the cleansing products that we use every day.
Ordinarily, soaps are made from just a combination of fats and alkalis. But most of the brands of soaps that we use today also contain deodorizers and perfumes. Others contain various chemicals to enhance their germicidal effectiveness. Whatever the composition, all soaps remove dirt. In hard water, however, soaps are poor detergents.
Soaps that are touted as skin moisturizers – and are therefore high in oil, fat and cold cream contents – are less effective at cleaning inasmuch as a cleansing product cannot possibly take off dirt and deposit moisture-retaining fat or cream at the same time. On the other hand, antibacterial soaps, which their manufacturers claim to be quite effective at protecting against bacterial infections or even at destroying viruses, are actually no better than ordinary soaps; they can be effective for those who have an open cut or are immunocompromised, the reason why these soaps are used in hospitals.
The effectiveness of soaps, as far as reducing microbes from skin or clothing is concerned, hinges on the mechanical eradication of microorganisms. Since soaps reduce surface tension, the wetting power of the water in which soaps are dissolved is increased. This makes soapy water emulsify and disperse oils and dirt more effectively. The microorganisms become ensnared in the soap lather and are then removed by the rinse water.
More effective than soaps, as cleansing agents, are surfactants or what are also known as synthetic detergents. Surfactants do not produce deposits with minerals found in hard water; neither do they form precipitates in acid water. They are widely used in most of the cleansing products that we use daily, including shampoos, dishwashing pastes or powders, and laundry detergents. Most surfactants destroy bacteria quite effectively.
The bactericidal and fungicidal powers of surfactants are exceptionally high. These are evident in most dishwashing pastes or powders which usually leave a film on dishes if not rinsed thoroughly; or in most laundry detergents which leave a residue on clothes that may cause allergic reactions to sensitive skin. For this reason, surfactants are used as sanitizing agents in food-processing plants, dairies, and dining establishments.