How does soap work scientifically

S how of hands: who has become infinitely, intimately more familiar with soap recently? If was the year we learnt to wash meticulously in between our fingers and all the way up our arms, it was also the year we discovered just how long 20 seconds in front of a bathroom mirror can be.

But have you ever stopped to wonder how the humble bar of hand soap actually works? At its most basic, hand soap is just a combination of fat or oil with an alkaline substance. The first people we know of to lather up like this were the ancient Mesopotamians, who mixed animal fat with water and wood ash to produce a substance that, while no doubt greasy, smelly and hugely unpleasant, could also spirit away dirt and grime in a manner that must have appeared borderline miraculous.

At its most basic, the wood ash splits the animal fat or oil called triglycerides into molecules called amphiphiles. These amphiphiles have one end that loves water, and another that hates it. You may not know Thordarson from a bar of you-know-what, but he actually went viral in early thanks to a Twitter thread on how soap works against virus particles, so he knows a thing or two about the topic.

Once you rinse your hands with water and lather them up with soap, the amphiphiles get to work. The hydrophobic ends want to avoid the water at all costs, so they start to bunch up next to each other, eventually forming a sphere with the hydrophilic ends facing the water and the hydrophobic ends inside.

But amphiphiles are also attracted to other non-water molecules, such as dirt, grease, bacteria, dead skin cells — even viruses. Then the amphiphiles form little spheres around the spilled contents, ready to be washed down the drain when you rinse your hands. What even is soap? First, a history lesson. Humans have been using soap for a long, long time. The earliest recorded evidence of the production of soap dates back to around BC in ancient Babylon. Long before humans understood modern chemistry or biology, they noticed that certain materials, when mixed with water, did a much better job of cleaning than water alone.

At the most basic level, soap is a special type of salt derived from vegetable or animal fats or oils—for example, tallow rendered beef fat , coconut oil, and olive oil are all popular soap bases. The oil or fat is combined with an alkaline metal solution, which breaks it down into the salt.

Depending on additives, byproducts, and materials used, the final soap product can be solid, liquid, thick, thin, oily, or greasy. All types of soap do the same thing: remove dirt and the disease-causing germs it contains. So, how does soap clean the dirt, grease, and oils off of your hands? This is important to understand for handwashing, because when disease-causing germs in fecal matter or dirt get on your hands after using the toilet or touching a contaminated surface, they mix with the natural oils on your skin and stay there.

The water slips right off without mixing, just like it does with cooking oil. Because soap is salt derived from an oil or fat, it has a unique chemical structure that looks like a balloon. The soap molecule can therefore act like a double-agent: the salty end is attracted to water, while the fatty tail is attracted to the dirt or oil.

When you mix soap with dirt and water, the soap molecules break up the dirt and the bacteria it contains by forming circles around individual droplets—the fatty chains go in the middle facing the dirt, while the salt balloon tops form the outside of the circle facing the surrounding water. The wheel-like structure formed by the circle of soap molecules around the dirt or oil droplet is called a micelle.

These molecules are called surfactants ; the diagram below represents a surfactant molecule. The head of the molecule is attracted to water hydrophilic and the tail is attracted to grease and dirt hydrophobic.

When the detergent molecules meet grease on clothes, the tails are drawn into the grease but the heads still sit in the water. The attractive forces between the head groups and the water are so strong that the grease is lifted away from the surface.

The blob of grease is now completely surrounded by detergent molecules and is broken into smaller pieces which are washed away by the water. You can find out more about how detergents work here. The detergent molecules also help to make the washing process more effective by reducing the surface tension of the water. Surface tension is the force which helps a blob of water on a surface hold its shape and not spread out.

The surfactant molecules of the detergent break apart these forces and make water behave, well, wetter! Bubbles and soap films are made of a thin layer of water, sandwiched between two layers of soap molecules. You can make giant bubbles by mixing these ingredients together:. Use your hands to make a hoop-shape. Dip them in the bubble solution and blow gently but firmly. Using this method you should be able to blow bubbles up to about 60 cm in diameter!

Dryness not sharpness breaks bubbles. Blow a large bubble then try putting your fingers inside it. If your hand is wet you can touch and even place your hand inside the bubble without bursting it! Make a large hoop of string about 1 metre in diameter and tie 4 small loops at the corners to make handles. Dip this into the soap solution and with a friend pull the handles apart to form a giant soap film.

Trying shaking one end and watch the wave travel along the film. Wet a tray or the kitchen work-surface with your bubble solution. Using a straw, blow a large bubble.