Apparently your hair/hair follicles have three cycles;
In the first cycle (the growing cycle) lil' baby follicles are being born, and are growing fast. So your hair grows it's fastest in this cycle (this is why you notice your hair taking longer to grow as it gets longer in length.) It usually lasts a year, but can last longer or shorter depending on genetics,
Then your hair will go into the second cycle, which is pretty much just a transition stage where the hair stops growing, and some of the follicles are replaced, for about two to three weeks.
After that the final cycle the hair dies, and some falls out (sounds scary, but is normal for everyone) the hair that doesn't come loose (most of it) is fully keratinized club hair, that, with it's buddies, will make a beautiful dread, and make everyone happy! But the hair that does come loose wont have anywhere to go, will stay in your hair, and the white will be follicles exposed.
Good news though, this is the shortest cycle and after it's done you'll have 2-3 years of steady growth. And I assume after your dreads mature, the cycles will be of little consequence, because they'll be settled and the roots will allow more room. I'm not certain though. I'm sure someone will.
I'm sorry I'm horrible at explaining this, its what I remember from researching hair loss in men (i was scared i was going to go the way of my father :P) but this applies for both genders!
Anyway, much love, and don't worry about it too much.