Strannegård Ö, Strannegård I-L, Allergy (2001) Vol. 56 #2, p.91-102.
Review of research into the causes of the increasing prevalence of allergies. Many reasons investigated, but none proven.
Author proposed that a major factor is a lower “microbial load” when young compared to good old days, i.e. today’s (perceived) higher hygiene standards present less chance for the immune system to be stimulated regularly at a young age (less stimulation of T-helper¹ cells). This is suggested to prevent ‘hyperactivity’ later in life.
This may be one of many possible factors. However nothing was proven.
Innocent causes of allergies should continue to be monitored.