Hair coloring by lay people may not be sufficiently accurate. Hair that has been damaged by excessive exposure to chemicals is considered "over-processed". This results in dry, rough and fragile hair. In extreme cases, the hair can be so damaged that it breaks off entirely. The main cases of hair breakage are: Lack of moisture and oils, poor diet, stress, over processing or illness. Skin and fingernails are made of a similar type of keratinized protein as hair. That means that drips, slips and extra hair tint around the hairline can result in patches of discolored skin. This is more common with
Hair cell mice bred to be missing the gene grow more hair cells than control mice that have the gene. Additionally, the sonic hedgehog protein has been shown to block activity of the retinoblastoma protein, thereby inducing cell cycle re-entry and the regrowth of new cells. The cell cycle inhibitor p27kip1 (CDKN1B) has also been found to encourage regrowth of cochlear hair cells in mice following genetic deletion or knock down with siRNA targeting p27. Research on hair cell regeneration may bring us closer to clinical treatment for human hearing loss caused by hair cell damage or death. Hair cell Hair cells