1. Why Soap Struggles in Water Containing Calcium and Magnesium
Soap has a specific weakness when it meets water that contains dissolved calcium or magnesium. When soap binds with these minerals, it changes into a hard clump called metal soap. This is what people often call "soap scum." It is explained as a cause of dirt in bathrooms and yellowing on clothes [5].
Water that has high levels of calcium or magnesium is called hard water. In hard water, the problem with soap becomes very noticeable. Synthetic detergents are said to contain ingredients that make it difficult to form this scum, even in hard water [5].
The main worker in any cleaner is a tiny particle called a molecule. This molecule has one part that likes water and another part that likes oil. These particles are known as surfactants. They are so small that they cannot be seen with the naked eye.
If synthetic detergents can fix soap’s weakness, they seem very useful. However, the reason synthetic detergent was born was not just to improve on soap. There was a different reason for its creation.
When looking at safety and environmental impact, opinions differ depending on who is promoting which product. Some sources argue one way, while others argue another [5].
2. How Synthetic Detergent Was Developed in Germany During World War I
Synthetic detergent is said to have been developed about 100 years ago in Germany, during the time of World War I [3].
Soap is made from animal or plant oils. At that time, there was a severe shortage of edible oils in Germany. It became difficult to secure enough oil to turn into soap [1][2].
Because of this shortage, people searched for cleaning ingredients that did not rely on oil. This search led to the creation of early synthetic surfactants for washing. Alkyl sulfate (AS), which later became widely used, is one member of this group [1].
The order of events is important here. Synthetic detergent was not born to fix soap’s weaknesses. It was born to survive a shortage of raw materials.
3. Monogen, Japan's First Household Synthetic Detergent, in 1937
The first household synthetic detergent recognized in Japan is said to be "Monogen," sold by Dai-ichi Kogyo Seiyaku Co., Ltd. in 1937 (Showa 12) [1][3]. It was a neutral detergent designed for washing wool products.
Later, in the early 1950s, Kao Corporation released "Kao Powder Laundry." The National Museum of Nature and Science explains that this product greatly changed the previous norm of washing clothes with laundry soap [4].
The year of release differs slightly depending on the source. The museum’s database lists 1951, while other materials say 1952. This article refers to it as "the early 1950s." The product name later changed to "Wonderful" [4].
4. How Synthetic Detergent Production Passed Soap in Japan in 1963
In 1963 (Showa 38), the production volume of synthetic detergent in Japan exceeded that of soap [1][2].
Some materials cite the spread of electric washing machines and television commercials as reasons for this popularity. This is introduced as one possible explanation among others [2].
In any case, it took about 10 years from when clothing detergents were first sold in the early 1950s for the ranking of production volumes to switch places.
5. Bubbles in Japanese Rivers: The Problem of Detergent That Does Not Break Down
As detergent use spread, bubbles became noticeable in Japanese rivers around 1961 (Showa 36). This became a major social problem [1].
The cause was linked to the ingredient used in detergents at that time, called ABS. This ingredient had a branched shape, making it difficult to break down naturally. Additionally, sewage treatment systems were not fully developed, so wastewater flowed directly into rivers [1].
As a result, manufacturers switched to straight-chain types (LAS or soft type) that do not branch. By 1971, it is explained that the proportion of soft-type detergents reached 97% [1].
However, switching ingredients did not completely remove the problem of water pollution.
6. Red Tides in Lake Biwa: Phosphorus, Local Ordinances and Phosphate-Free Detergent
After 1977, red tides occurred in Lake Biwa. When too many nutrients enter a lake, organisms that cause red tides increase easily. This state is called eutrophication and became a serious issue. The phosphate salts in detergents are considered one of the causes [7].
Shiga Prefecture established the "Lake Biwa Ordinance." It banned the use, gift, and sale of household synthetic detergents containing phosphorus. The ordinance came into effect on July 1, 1980 [6].
In that same year, 1980, phosphate-free detergents were sold. These used zeolite instead of phosphate salts. It is explained that in current Japan, household detergents are almost 100% phosphate-free [1].
The ingredients of detergent have been reviewed each time for different reasons: oil shortages, river bubbles, and lake red tides.
7. How You Can Investigate Soap and Detergent Yourself
You can start by comparing the ingredient labels on the detergents and soaps you have at home.
Look at the back of laundry detergent and soap boxes. Copy down the names in the ingredients section and compare them. You can also look for the type name of the "surfactant" or any label saying "phosphate-free."
If you line up boxes for other products, like kitchen detergents or body soaps, you can see where the same names appear.
The full text of the "Lake Biwa Ordinance" can be read in Shiga Prefecture’s collection of regulations [6].