I'm just posting this personal experience for information.
I live in the UK and have suffered from allergic rhinitis since my teenage years (now 66) and have needed four endoscopic surgeries for nasal polyps and turbinate reduction, including long bouts of anosmia. Two years ago I was also diagnosed with late onset asthma.
The key trigger for all this is my allergy to house dust mite which I have found exasperatingly impossible to deal with despite exhausively following all the official advice to minimise exposure.
A few weeks ago I purchased what for me is a remarkable and fairly new to the market air purifier manufactured by Dyson, the Dyson Cool Tower. I have this running in the bedroom 24/7 (door and windows closed) and from Day 1 this has transformed my life. No morning awaking with itchy watery eyes and nose. No scratchy breathing, sneezing or coughing and for past four weeks no need to take my daily Flixotide steroid inhaler, although I am continuing to use Flixonase nasal drops.
Another bonus is that my sense of smell has returned!!!
I am due an annual asthma checkup soon so it will be interesting to see what the medical advice will be.
Not sure if I'm allowed to post this here but below is the Dyson link. Warning – it's not cheap and there may be others around just as good.