Dust allergy and hay fever open windows or not?

[OompaLump]

Son has severe allergy to dust and pollen but I'm struggling to know what to do for the best.
His room gets very hot and I have been reluctant to open the windows due to the very high pollen count but the humidity in his room could be encouraging dust mites.

Do I open the window for half hour to air the room but run the risk of pollen getting in?
What do people do with both allergies where opening the windows is advised to air the rooms but advised not to for pollen allergies?
Obviously I'd open on low pollen counts but the pollen has been very high for weeks

The advice given to me by my specialist many years ago was that windows could be opened from 10am till 6pm and during the night if necessary

The rationale for this is that pollen starts falling to ground level and is able to float in through windows when the day cools and it starts to come down to ground level.

This would usually have occurred by 10pm so windows can then be opened for the night but should be closed early in the morning

In reverse as the day warms pollen rises and so is above house level after 10am when windows can once again be opened

In such cases, you need to come up with alternative options for cleaning the air in the house and circulating. But again, if you believe the read here greenductors.com/what-will-the-first-breath-of-your-baby-be-like/, then you should also follow the cleaning regularly. Then, as a result, you can achieve the desired effect for the health of the child.