The practice among Buddhist monks of shaving their heads is symbolic of non-attachment, particularly to the ego or self. The head hair, or "kesa," is for many Buddhists one of five bodily features that obstruct knowledge of one's eternal nature. Traditionally, monks will shave their heads as part of their ordainment or, as the Japanese put it, "tokudo," which means "going to the other side."
Following ordainment, it is common in some traditions, such as Jodo Shinshu, for monks to allow their hair to grow again. In many other traditions, however, it is expected for monks to keep their hair limited to a length of two finger widths. To this end, it is common to shave the head at least once a month and sometimes once every 2 weeks. The beard is also removed.
According to Buddhist history, Siddhartha Gautama shaved his head as part of his renunciation of palace life. For many monks, therefore, shaving their own heads is a symbolic means of embodying their principal spiritual teacher. Some Indian Buddhist ascetics go even further and tear their hair out, rather than shave it off.
Some Buddhist nuns also shave their heads but, as with monks, it is not a universal practice. A similar observance by many Buddhist monks and nuns is to avoid removing or dying gray hairs, which serve as a reminder of the physical body's impermanence.