McMoria

Yep, windows open help, and for me it's preferable anyway to have some air flow. My concern in the OP was just health effects of relative high humidity in low temperatures which it seems are minimal. Cheers

This is the critical aspect for me, Eg, the humidity inside is 80, and so is outside. But it's 2 degrees C or something. I'm figuring out if I have to worry about it with regard to respiratory issues (sounds like I don't as there just isn't enough moisture to worry about) and with regard to mould etc, which I am less confident about. The cooling/reheating process you mention seems to be at odds with Studiot's comment on mould/spore generation and suggests simply warming but I may need further details from Studiot regarding that. This was initially an issue because, the morning after the first sub-zero night I spent in the van, the polyester blanket over my duvet was soaked, the van was freezing, and the CO2/Fire alarm went off in some crazy error mode. The only difference was that I had shut all the windows. Now I leave them open a crack and don't seem to get it as bad. I guess my own body's perspiration had condensed on the non-absorbing polyester and in the circuits of the alarm.

Thank you for your reply and I understand the statement. I suppose to clarify my question I'm looking for an idea of the correlation coefficient with regard to relative humidity and temperature where potential health concerns occur, be they respiratory, mould or bug related. For instance it could be 99% relative humidity but at -3 degrees C I'm not going to be worrying about mosquitoes. Most information I can find relates only to high humidity/high temperature scenarios.

I'm trying to understand the effect of humidity in my living environment- a camper van. My limited understanding is that the relative humidity in my camper van should be roughly between 40-80%. And an ideal way to maintain lower humidity is apparently to increase the air flow by opening windows. If the relative humidity outside is over 80% (which it is: 5 degrees C/ 83%) would this even help? And isn't it unhealthy simply being outside in this case?