Dirty hair is often times confused to be a good practice for growing black hair. It’s easy to see why this mistake is made, but dirt on your hair in no way encourages growth or length retention.
Dirty hair is associated with growth for some people because when you don’t wash your hair as often there is less manipulation and less manipulation means little room for breakage and ultimately length retention.
This does not mean that dirt is growing your hair. In fact, when your hair is dirty it is hard for any moisturizing products you use to work because buildup makes it hard for any product to penetrate the hair.
What this really means is washing your hair less frequently fits better into your regimen. While washing hair once a week works for some people many others find more success in going 3 weeks without washing.
Oh and just because your hair is washed less often this does not mean that it is dirty. Cipriana of Urban Bush Babes washes her hair monthly and her aim is definitely not dirty hair.
(read more about her routine at: http://urbanbushbabes.com/2011/06/my-7-step-weekly-routine-part-2/)
This method makes sense for her hair texture, length, and preference. If you find that something like this works for you then go for it. However if you are washing your hair less often put a smaller amount of products and lighter products in your hair to prevent buildup.
When your hair feels like it desperately needs a wash, wash it. Keeping your hair dirty will not make it grow. You can have a routine of less frequent washes, but dirty hair should never be your goal.
Cassandre covers this in her video and gives a very good response to this frequently asked question