Personal hygiene is important because it helps prevent and control diseases, according to the Centers for Disease Control and Prevention. This includes hygiene of all kinds, such as, facial, body and dental cleanliness.
Insufficient practices conducive to good health involving the scalp or hair can lead to head lice. Lice can be more pervasive. Body lice affects bodies that haven't been thoroughly cleaned. Poor bodily cleaning can also lead to scabies and ringworm.
Being negligent in cleaning the feet properly can lead to athlete's foot. The hands aren't immune; failure to sufficiently clean the hands on a frequent basis can lead to diarrheal illness.