Facial hair in ancient Egypt, especially beards, remains a mystery in later periods, with significant religious implications. 
History.
Facial hair had a varied history in ancient Egypt. During the pre-dynastic era and the early years of Egypt’s historical formation, men favored beards. This is evident in depictions such as on the Narmer Palette. Officials and rulers of the Ancient Egyptian kingdom, such as Prince Rahotep, were portrayed with moustaches, and full beards widely appear on mummy masks from the First Intermediate Period and Middle Kingdom, like those of the 12th dynasty mummy named Ankh. However, by the early dynastic period, it seems that shaving became fashionable, at least among the noble elements of society. Later, shaving spread to the rest of the population, who had a certain understandable tendency to mimic the practices of the elite society. In fact, the lack of a beard became a sign of poor social standing, except in the case of mourning or preparing to embark on an expedition abroad.
Symbolism.
However, there remains a mystery surrounding facial hair that is clearly present in art and religion. Despite the clear decline of facial hair during life, the beard was considered a divine symbol for the gods, whose beards were often depicted as "like lapis lazuli." According to this religious formula, the Egyptian king expressed his status as a living god by wearing a false beard, tied in place during certain occasions. These false beards were often wider at the bottom, as seen in the triple statues of Menkaure. This type of beard was widespread in royal depictions, with even Queen Hatshepsut portrayed with a false beard.
In death, kings were frequently depicted wearing the divine Osird beard, a long, narrow beard braided into several strands with the end sticking out, as seen on the gold mask of Tutankhamun. Even non-royal men who died were often depicted with short beards resembling strands. However, this is not always the case, as the deceased king did not always appear with this type of beard.
Such beards in ancient Egyptian art, regardless of context, always seemed to represent divinity, although not all male gods wore these beards.
Given the divine nature of beards, one of the questions that arises is why they fell out of popularity early in Egyptian history. Perhaps certain types of beards resembling those of the gods and the false beards of the living king were forbidden, or simply fell out of fashion due to religious reverence. However, it is more likely that the reason was the ancient Egyptian obsession with order, elegance, and cleanliness. Throughout much of ancient Egyptian history, it seems that the poorest of the poor continued to wear beards, and others likely wore them regularly. Therefore, there appear to have been legal restrictions on beards.
Also of great interest, outside of religious contexts, is the fact that beards in Egyptian art often signified the foreign nature of the individual. Egyptians often depicted their enemies with beards. Given the Egyptian practice of capturing foreigners, this may explain some of the popularity of shaving, as well as why officials sometimes refrained from shaving when traveling abroad.
To summarize, beards were a significant aspect of ancient Egyptian art, as they provide us with clues about the nature of the individual, whether royal or commoner, foreign or Egyptian, god or man, depending on the type of beard, whether the king was depicted alive or dead.