Soap, due to its chemical properties, such as amphipathicity, can destroy the cell membranes of bacteria and other pathogenic cells, as well as the shells of many viruses.
Parents, doctors, and even soap commercials all advise washing hands with soap upon returning home and before eating. Washing your hands with soap is a vital hygiene practice, especially during flu season. The reason for this practice is the ability of soap to “kill” germs.
It’s amazing that something as mundane as soap can be our best defense against deadly viruses. So what gives soap its ability to protect us from germs? And does soap really “kill” the virus?
What is soap?
Soap is the slippery thing we use to wash our hands. True… but chemically speaking, soaps are salts of fatty acids. They are produced by the hydrolysis of fats and oils (triglycerides) from natural sources using an alkali solution. Alkali is alkali obtained by preparing an aqueous solution of caustic soda. This process is known as saponification. The pH of the soap is in the range of 9-10.
All soaps are essentially surfactants and are composed of amphiphilic molecules. This means they have two parts: a hydrophilic (water-loving) head and a hydrophobic (water-hating) tail.
Surfactants are special chemical compounds that can change surface tension between different phases.
The carboxylate group of soap forms a polar head that is attracted to water molecules. Meanwhile, the non-polar tail containing the aliphatic chain is repelled by water and has an affinity for lipids and oils. This dual nature of soap allows it to dissolve both polar and non-polar molecules.
How does soap work?
To understand how soap kills germs, you must first understand how they operate under normal conditions. With that in mind, let’s take a look at how soaps and detergents wash clothes so effectively.
Detergents easily remove dirt and grease from clothes due to the action of amphiphilic molecules. When you add detergent to water, the polar head orients itself towards the water phase. Meanwhile, to get away from water molecules, the hydrophobic tail targets non-polar molecules such as oils.
The hydrophobic tail attaches to dirty and oily stains to prevent contact with water. At the same time, the hydrophilic head is connected to the water molecule. The soap then strips the oil from the surface, orienting itself in a circular pattern around oil particles known as micelles. These micelles accompany the oil molecules to the surface of the water. Here, the lather traps dirt and oil, allowing it to be rinsed off with water.
But what about viruses?
We can say that viruses are like oil molecules. How, you ask? Well, a virus is essentially genetic material wrapped in a protective layer called an envelope. These shells are made up of fats or, scientifically speaking, lipid bilayers. They also contain an integral part of the virus: protein spikes. These spike proteins cling to receptors present on host cells, allowing the virus to infect them.
As with washing grease stains from clothes, soap molecules attach to viruses and other microbes. When you wash your hands with soap and water, the hydrophobic tail of the soap starts looking for a place to get away from the water molecules. When they find the virus, the soap molecules begin to surround it. The hydrophobic tail adheres to the bilayer lipid wall of the virus and detaches it from a given surface, such as skin.
See also: The most dangerous bacteria
That’s not all. The hydrophobic tail penetrates further into the virus, trying to get away from the water. Just like popping a bubble with a pin, the tail opens up the outer wall of the virus. This breaks down the virus, and its contents fall into the soapy water. The remains of the virus are washed off when you wash your hands.
Soap “kills” the virus?
Although many soap advertisements claim that soap “kills” germs, this is technically not true. Soap simply breaks the virus apart and removes it from the surface. So much so that in the end the virus still technically remains, but only in parts, without cell walls and spike proteins.
Contrary to what many people think, soaps are far more effective at killing germs than alcohol-based sanitizers. Disinfectants do kill viruses and germs, but they cannot wash away the virus. Instead, they leave sterile dirt and dead viruses on their hands. Also, since they are only 99.9% effective, they can also leave some active viruses on your skin.
Hand sanitizers can be a good substitute for soap and water. However, when possible, soap and water should be used to wash hands. Health authorities recommend washing your hands with soap and water for 20 seconds to successfully wash viruses and germs off your hands.