Doors will swell when the humidity in the house rises. If you've recently installed a humidifier or turned an existing one one, maybe it needs to be set a little lower. 35%, give or take, should keep everyone (plants and animals included) happy.
Also, depending on where the doors are, if for example, the bathroom door is sticking, it could be from excess humidity in the shower. Installing a fan-vent, opening a window, or just leaving the door open will help, or perhaps cure your problem. For entry doors that are exposed to the 'elements', that can contribute to the problem too. And lastly, the material that the door is made of will add to your problem too. The softer the wood, the more readily it absorbes. If your doors are unfinished/unstained, consider finishing/staining (and sealing them) to keep the moisture out. The same goes for the door JAMS all around the house.
My best to ya and hope this helps.
Jay J -Moderator
PS: God Bless America!