I suffered from hay fever for 30 years of my 35 year career and looked forward to deployments during the season as it cleared up. When abroad on detachments it also cleared up so it shows that it is UK pollen that I was affected by. May not apply to all. I am currently in texas where most folks suffer from allergies but I find it is very much reduced over being back in the UK.
Mine started off mildly but got worse as I got older and sometimes caused astma attacks which would not be good for aircrew. I know the forces don't recruit astma sufferers at all but mild hay fever
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bj