It can be traced in part to air pollution, excessive hygiene, changes in diet and environment, and that people have become genetically mismatched to the world around them.
Times, Sunday Times (2008)
About 40,000 people die prematurely from illnesses linked to air pollution each year in Britain.
Times, Sunday Times (2016)
A study from Rice University, in Texas, found that the smoke from a grill could add to air pollution - that can lead to bouts of asthma.
The Sun (2014)