The exact origin of soap is unknown, and today there are different interpretations about it. Some references place the origin in Babylon in 2800 BC, in Egypt in 1500 BC or in Phoenicia in 600 BC (Ditchfield, 2012). Other studies directly believe that locating the exact origin is practically impossible (Gibbs, 1939; Hunt, 1999). What is known today is that the knowledge about the cleansing character of plant ashes was known since ancient times.  In addition, many relevant details are known about the development of such an essential product as soap. 

 

For example, the origin of soap seems to have been linked to the utilization of raw materials resulting from other processes. Soap in its rudimentary state arises from the combination of animal fat with ash. A mixture that could have been produced, for example, from slaughterhouses. The combination of the two materials produced a process known as saponification, about which many details have been learned in the course of history thanks to scientific progress. 

 

It is also known that soap was first used to wash fabrics and clothes and was later used for personal hygiene. We also know that Galeano, a Greek physician from around 130-200 A.D. who achieved fame in the Roman Empire, spoke of the value of soap for cleansing the body to prevent disease.  From the 9th century onwards, soap production is known to have emerged and developed in centers such as Marseilles (France) and Savona (Italy) with a type of soap that represented a leap in quality by incorporating olive oil in the production process, through a very slow cooking process (Wilson, 1954; Hunt, 1999). Not long after, Castile soap was created in Spain, which stood out for the quality of its barrilla, that is, for the almajo ashes that were used as alkali (Eslava Galán, 2016). 

 

The history of soap is full of curiosities that, seen from today, can be shocking. For example, John Hunt relates that in its origins soap had nothing to do with the current soap, as it was not pretty and did not always smell good (Hunt, 1999). Moreover, its expansion was very slow. Lucock Wilson narrates how, in spite of the progressive improvement in the production processes, in a century like the 16th, it was still a luxury product and that even "Queen Elizabeth I (of England) took only one bath a month" (Wilson, 1954, 6). Although it was even stranger that Louis XIV (1643-1715) bathed because he thought that this act transmitted diseases.  

 

The heyday of soap occurred at the end of the nineteenth century and the first half of the twentieth century and was accompanied by a change in the conception of hygiene (Ward, 2019; Wilson, 1954). It was not until 1847 that it was known, thanks to the Hungarian physician Ignaz Semmelweis, that hand washing by physicians attending births was a life-saving act by reducing the mortality rate in the maternity ward. This evidence was rejected by the physician's colleagues and was not validated until the following decades when the chemist Louis Pasteur presented his discoveries about germs.  

 

Moreover, the main reason for this heyday is linked to the development of great advances in the field of chemistry. Science advanced in the knowledge of the chemical processes accompanying saponification and the causes behind the reactions produced as a result of the combination of fats and ashes. One of the key discoveries was made by Nicolas Leblanc, who developed a new type of alkali, derived from salt, which allowed it not to be extracted from wood, constituting a significant advance in avoiding deforestation (Gibbs, 1939, 178-179). The development of soda initiated by Leblanc was later improved by the Belgian chemist Ernest Solvay (Ditchfield, 2012). The 19th century saw another series of advances that would form the basis on which modern manufacturing technology developed (Gibbs, 1939). In this period, mechanical power and steam were applied, which allowed production to increase very significantly. Another key scientific breakthrough was the studies of the chemist Eugene Cheureul, who made it possible to discover details about the saponification process by observing the presence of what he called glycerin (Ditchfield, 2012). As a result of these discoveries, the productive development was immense and with it the generalization of the use of soap to broad layers of the population to the levels we know today (Wilson, 1954).