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If I recall correctly, nails (finger nails or toe nails) grow by adding matter at its base. So for instance, if you would draw a dot at the very bottom of your nail, it would end at the top in a couple of weeks.

I was wondering how this works with hair. Is new hair added at the bottom and the old hair 'pushed' away? Or does hair consist of layers that always try to get further and further (that would mean longer hair is thicker than shorter hair). And is this wayof growth similar to how grass grows?

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In hair and nail growth new cells are added to the bottom. These cells are produced at the follicle. There are three stages called:

  1. Anagen : active growth
  2. Catagen : end of active growth
  3. Telogen : total stop of follicular growth

I don't know what you mean by like grass but both nails and hair have a first in first out order.

Feathers present a contrasting case: the outermost portion is the most recent. Feather growth is relatively more complex. This article is a nice read on feathers.

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Well, does grass grow in a similar manner? First in, first out? – Bram Vanroy May 27 '13 at 9:09
3  
plants grow differently.. the tips grow.. its opposite to hair growth – WYSIWYG May 28 '13 at 10:40
    
And all hair cells are all dead cells... – Barun Jul 22 '14 at 11:32

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