Buddhist monks and nuns shave their heads for various reasons, including religious, practical, and symbolic ones. Here are some of the reasons cited in the search results:

• Religious: Shaving your head (and face) is part of Pabbajja, which is when a person leaves their home and “goes forth” to live the life of a Buddhist renunciate among ordained monks. It is a paramount step to becoming a monk. Shaving the head is one of the rules the Buddha laid down for his monks and nuns. It is one of the key indicators of renunciation showing that a person has given up ordinary life and will live outside of social conventions.

• Practical: Going bald makes life a lot easier. Without hair, you spend less money on shampoos, hair products, and haircuts. In addition, no more harsh chemicals or medical shampoos that damage your scalp.

• Symbolic: Shaving our head symbolizes cutting off confusion, hostility, and attachment—what the Buddha called the “three poisonous attitudes.” These three mental toxins poison our well-being and our relationships with others. Confusion makes us ignorant about the causes of happiness and the causes of suffering. Hostility and anger ruin our relationships with others, especially with those we care about the most. Whenever we monastics shave our head, we think about cutting off our own and others’ confusion, hostility, and attachment. Cutting our hair becomes a way to recall the purpose of our life. Hair is an aspect of the identity and is more often than not, associated with vanity. To find out who you truly are underneath the many layers of conditioning society has put on you, the hair is removed so that this level of identity is also removed. It puts everyone on the same level.

In summary, Buddhist monks and nuns shave their heads as part of their religious practice, to simplify their lives, and to symbolize their detachment from worldly desires and their commitment to spiritual growth.