I am on vacation for a week. I left a couple windows cracked in my 2 bedroom apartment. I also left all the doors inside the apartment open. I thought air flow would be good while I'm gone, but now I'm worried that some rainy days while I'm gone could cause the humidity to go up and down. The tempurature will be between 50 (at night) and 70 during the day, but the humidity will rise and fall quite a bit. Should I be worried about damaging the apartment? I could try to have someone come and close the windows for me but it would be really difficult to do this - so unless it's critical I would rather just leave them. Thanks for any advice.
Normal humidity should do no harm to anything that's been properly made. Remember, humanity has lived with poorly sealed houses in humid climates for centuries, and our belongings have adapted to deal with that.
Woodworkers, for example, are very aware that wood expands and contracts as it gains and losses moisture, at different rates along and across the grain. That would cause trouble if everything was firmly held in place, so some connections are actually designed to slide a bit.
Other things make other adaptations, but o in general as long as materials aren't going to be soaked they will do OK.