Hay Fever

MrJ suffers too, his medication helps a lot, we’d rather have washing dried outside than risk mould inside which may cause other health issues.

I was very smug because everyone in the family had hay fever except me. I've now developed it as an old age person! Lots of sneezing and itchy nose stuff. It has been bad this year. I never thought about the effect on clothes from hanging them out

It may be true.

But I read os much of "research sys this" and "the answer may be that", that just doesnt apply to people I know, including family members.

In this particular case, a family member gets hay fever. But lives in a flat. So doesnt ever hang washing outside.

I would dry sheets outside, but never pillows.

Another tip is to reduce the amount of unnecessary 'fabric' in your home, e.g. padded fabric headboards on beds. Yes, I know, they look lovely. Too may cushions? They say favourite soft toys should sometimes go into the freezer. Haven't tried that. Vertical instead of horizontal venetian blinds.
Good luck resolving the problem.