Why do people as they get older start to have a foul smelling natural smell?

Question: Why do people as they get older start to have a foul smelling natural smell?
- Keywords:
  age,
  foul,
  older,
  smell
Asked by bethj to Carolyn, Peter, Richard, Sara, Siana on 16 Nov 2015.
- Richard Unwin answered on 16 Nov 2015:
  
  I don’t think anybody knows but it is real. Researchers in Philadelphia once did an experiment by taking ‘odour’ samples from young and old people by sewing special pads onto T-shirts and asking young and old people to sleep in them for 5 nights. They then collected the samples and asked people if they could tell the age group – most people identified the ‘old age smell’ every time!
  
  Nobody knows what causes this – theories range from changes in metabolism, changes to the sweat glands or skin bacteria, or changes in personal hygiene.

Question: Why do people as they get older start to have a foul smelling natural smell?