What are the chemical properties of the soaps

Fascination with chemistry

Soap's history goes back a long way

4,500 BC For the first time, the Sumerians made a kind of soap from alkaline vegetable ash and oil, which they used at that time as a healing ointment. The Egyptians also adopted the soap recipe later and refined the recipe. In addition to cleansing the body, soap was also used to wash clothes. In medicine at that time people believed in the healing properties of soap and used it to treat skin irritations and diseases. However, the supposed healing effect can be attributed to the fact that soap cleansed the skin. Because some diseases at that time were also due to a lack of personal hygiene. The Teutons and Gauls used soap as a cosmetic. For example, they bleached their hair with it or styled themselves with a soap pomade. In the 7th century, Arab tribes developed soap production further: They used burnt lime to make particularly strong soaps. In addition, heating and stirring the oil in potassium or sodium hydroxide until most of the water had evaporated and the oily mass solidified - this is how the first bar of soap was created.

In the Middle Ages, European soap makers produced perfumed luxury soaps - although these were initially reserved for the nobility. Plague and syphilis stifled the emerging bathing culture. As a result, soap was not used in the 16th and 17th centuries, and powder and co. Preferred for personal hygiene. It was not until the 18th century that soap and water were rediscovered to cleanse the body.

The high demand for soap at the beginning of the 19th century was then met with industrial production. This used the now synthetically produced sodium carbonate and sodium hydroxide. Soaps for the body contained high-quality oils, while hemp and linseed oil were inexpensive for washing and scrubbing.
 

Cleansing, but harmful?

Today we can hardly imagine that soap was once a luxury product. The soap we use has long since ceased to be the same as the original soap. The alkaline substances that a real soap contains have an alkaline pH value that is very high compared to the pH value of our skin. Our skin ideally has a pH value between 4.7 and 5.75 - i.e. in the slightly acidic range (pH value 7 is considered neutral). Soap not only cleans our hands, but can also damage them - it removes fat from the skin. As a result, it dries up. Today we usually wash our hands with solid and liquid substances that contain only a small amount of actual soap. Rather, synthetic detergent substances replace these and many additional substances complement today's soaps. For example, manufacturers add perfume, skin protective substances such as chamomile, or disinfectants. There are also “soaps” with a neutral or slightly acidic pH value to protect sensitive skin. These no longer contain any soap. Actually, we should rather refer to the “soap” as a “washing bar” or “washing lotion”. But one thing is certain: As in ancient times, these substances remove dirt and pathogens from our hands when we wash them.

Cover picture: © Alexander Raths / stock.adobe.com

Volunteer, Society of German Chemists

This article was published for the first time on FaszinationChemie on August 6th, 2020.