这里的brushing your hair regularly做了主语的成分,一般来说,动词放在开头加了ing都可以作主语,例如,Cooking anything you like is the other advantage of having separate accommodation.
当然,不仅仅是用于开头,在句中你也可以见到动词作名词的形式,例如,Choose either homestay or having separate accommodation.