Can seasonal allergies shorten life expectancy?

Allergies: Not likely. I am sure some days it must feel like they will. But, i would say no.

Severity dependent: Allergies if sever and left untreated could lead to recurrent bacterial infections as well as lung conditions and or infections that would mimic the effects of being a chronic smoker. In this way, yes.

No: Seasonal allergies can significantly affect quality of life, but not quantity of life. Although allergies cannot be cured, there is effective treatment--see an allergist to find out how.