The image of a small beard under the nose of Japanese people in World War II can be said to be deeply rooted in people's hearts, but now it seems that it is difficult to see Japanese people with this beard again.
This beard has a special name, called "sanitary beard". Sanitary hu was once popular in Germany, Japan and other countries in the 1930s and 40s, but it did not last long, and today, it is difficult to see anyone keeping a sanitary beard.

People in different eras have different aesthetics
Just as the Tang Dynasty people regarded abundance as beauty, while modern people advocated slimness, people's aesthetics are constantly changing with the development of the times. At that time, the sanitary beard was indeed once popular, but with the changes of the times, the sanitary hu no longer represented fashion in people's eyes, and even appeared to be somewhat funny, and people naturally did not grow this beard.
Germans used to love beards
To trace the connection between hygiene and fascism, we must first return time and space to nineteenth-century Germany. At that time, Germans loved a beard for ten minutes, believing that a thick and lush beard best reflected a man's masculinity. So beards became a trend, and whoever had a beard was the most beautiful cub on the whole street.
In this atmosphere, even our great teacher, Mr. Marx, is not exempt from vulgarity, and the classic image of a beard must be familiar to everyone.
Beards were replaced by "sanitary beards"
This ethos continued until The First World War. Due to the large-scale use of gas bombs in World War I, soldiers needed to wear gas masks for protection.
At this time, the drawbacks of the beard appeared, that is, the gas mask could not be stuffed, even if it was barely stuffed, the air tightness of the gas mask would also be affected, and once the gas penetrated into it, it was a fatal thing.
Between life and beauty, the soldiers unsurprisingly chose the former. They shaved off their proud long beards, but they were reluctant to shave them, so they left a handful in the middle of the people and chatted for comfort.
This beard is not only easy to wear a gas mask, but also easier to take care of than a large beard, clean and hygienic, and "sanitary beard" is also named after it. Next, a heavyweight related to sanitary beards must be invited, that is, the Nazi leader, Hitler, who has the iconic sanitary beard.
Because Hitler participated in World War I and personally experienced the benefits of sanitary beards, he developed the habit of staying sanitary beards after the war. Later, Hitler became the head of germany, with a large number of fanatical supporters, and even Hitler's beard was imitated by his supporters, so the sanitary beard became completely popular in Germany.
The Japanese followed suit, and the hygienic beard became a status symbol
As we all know, Japan is a country that is very good at learning and imitating. In ancient times, the object of their study was China. After the Meiji Restoration, the Japanese began to move closer to the more advanced West in all aspects. As a powerful fascist country, Germany was the object of Study for Japan, and in line with the principle of not refusing, the Japanese also learned the health hu.
Not only that, but the sanitary beard has also been given a new connotation by the Japanese. The Japanese believe that the hygienic beard has something in common with the spirit of Bushido, turning the hygienic beard into a status symbol. In Japan at that time, the sanitary beard was not available to everyone, but only those with a certain status could keep it. So we see that the Japanese with small mustaches are basically Japanese officers.
Since the sanitary Hu was mainly popular in the fascist countries of Germany and Japan during World War II, it was inevitable that it would be associated with fascism after the war. As the fascist clique disintegrated, people no longer had this beard with the label of fascist.
Speaking of which, there are some similarities between the Japanese who left sanitary beards and the Qing Dynasty people with long braids, which are both products of a special historical period. With the passage of that history, coupled with the changes in people's aesthetics, the sanitary beard, like the braid, gradually disappeared from people's sight.
Resources:
"Hitler biography" and so on