To not change the sheets...

[LostAtTheFair]

I have a guest coming next week. I changed the sheets after the last time the spare room was used, which was a month ago. Would I be U to let the guest use the clean sheets which have been on the bed for a month. I know that the guest is allergic to dust

Hoover the sheets/bedding?

I would say in a normal situation YANBU, however they have a dust allergy... I would change the sheets and vac the bed.

For next time you could steal my sneaky trick:

My DSis is dust allergic so I clean and re-make the spare bed and then put a mattress protector on over everything. Then, when she arrives, I dust, hoover and whip off the protector. Takes 5 minutes.

YABU

Be a nice host and clean the bloody sheets

Yabu I have a dust allergy and sleeping in a bed that's gathered dust for a month would leave me feeling rather rough. Itchy eyes, coldy symptoms, and generally a bad nights sleep impacting onto the next day.

Wash them this time and next time either chuck a mattress protector or a spare duvet over the top of it all or leave it unmade and give it a Hoover before putting the sheets on.

the sheets are clean?? you have a spread on top?? if I did anything special for a guest with allergies I would take the top bedding cover and air it outside for a few hours. do an extra dust in the room itself.
who has the time to wash clean sheets? or think that dust collects under clean bedding that no one has used since the last set of guests??
do people wash clean bedding that has been in a linen closet before putting it on a bed.

I would not be uncomfortable if we were the last people to sleep in the bed.. Not so sure about other people ...

YABU.

I change the bedding before new guests arrive (as in the day before/ day of arrival) then they stay on until next usage. So I do the same amount of washing/ changing as you but guests always get fresh sheets.

Well, since your guest is allergic to dust I think you should wash the bedding and thoroughly hoover the room. That's what I would do, anyway.

Do you want her sneezing/coughing/itching a rash all over your house and being miserable because you couldn't be bothered to change the sheets?