Why does our hair turn grey when we get old? Also, does something like this happen to other animals (or even plants?

Question: Why does our hair turn grey when we get old? Also, does something like this happen to other animals (or even plants?
- Keywords:
  ageing,
  animal,
  body,
  hair,
  plant
Asked by to Jennifer, Kim, Liam on 26 Jun 2014. This question was also asked by .
- Jennifer Stephens answered on 26 Jun 2014:
  
  Hi 12sarsat
  It’s to do with the melanin pigment that gives hair its colour. It happens to most people and when it happens depends on lots of things including genetics, hormones and age. External factors like pollutants and exposure to toxic chemicals can also make it happen quicker.
  
  Some dogs get grey hair, but others don’t. In plants, when leaves are getting older, chlorophyll disappears and other pigments like anthocyanins and carotenoids start to show through gives yellow and red colours.

Question: Why does our hair turn grey when we get old? Also, does something like this happen to other animals (or even plants?