There are two types of people who don't shampoo every day: those who don't wash their hair every day, and those who wash their hair with water most days but shampoo only some days.
If your girlfriend is in group 2, then your experience is relevant to the parent's post; if she is in group 1, then you haven't yet experienced the difference.
There are two types of people who don't shampoo every day: those who don't wash their hair every day, and those who wash their hair with water most days but shampoo only some days.
If your girlfriend is in group 2, then your experience is relevant to the parent's post; if she is in group 1, then you haven't yet experienced the difference.