In Hinduism, the mundan is one of 16 purification rituals known as Shodasha Samskara. The ceremony is believed to rid the baby of any negativity from their past life while promoting mental and spiritual development. According to religious texts and scriptures, a soul gets a human body after experiencing 84 lakh yonis. And it is said every yoni has its influence on human birth. The shaving off hair from a child’s head is a gesture of purification from the previous yonis and freedom from the past.ImageSource
Some like to emphasize that it improves the growth of the baby’s hair, The natural growth of hair on a baby’s head is uneven. Shaving off the hair from the baby’s head helps in proper and healthy growth of hair. Some ancient scriptures say it helps in stimulating proper growth of the brain and nerves.
The other scientific reason is that Vitamin D is made faster and in more quantity in the baby’s body when exposed to sunlight without clothes and hair. When a tonsured head is exposed to sunlight it absorbs the sunlight better.
Hindu men also shave their head off after someone dies in their family, mostly elder ones. It is believed that shaving off the hair helps men to let go of their ego. It gives them a sense of responsibility and reminds them to be obedient and become more selfless while performing their deeds.ImageSource
Hinduism has plenty of rituals and the person born in a Hindu family starts following the rituals right after his/her birth, this leads them to the path of salvation from the start of their lives.