The reason why interior doors can get so damaged is because they take a lot of abuse every day. Not just the humidity has an impact over them but also paint and rubbing against door frames. All problems that can occur can be easily fixed.
Because of the humidity, doors tend to expand and contract and this can cause them not to close properly. Handles and hinges also take a lot of abuse and must be repaired immediately. If you see that doors often have problems because of the humidity in the air, you might consider investing in a dehumidifier to get rid of the excess moisture. If the door sticks to the frame, maybe it needs to be sanded. To identify the places where the door has bumps just use cardboard to run it on the length of the door. If it doesn’t have enough space to pass through, then that particular spot needs to be sanded.
One other common problem is related to misaligned hinges. First of all check if the hinges are fixed properly in the wood with the screws. If the screws are loose then you should remove them, drill the holes and then use some sturdy wood filler. Then try to screw them back and better fix the hinges. Another problem may be caused because of the shallow hinges. They may also get damaged and bend. Just remove the door and use a small chisel to deepen the spot. Then reattach the hinges and place the door in its place. The opposite of this problem is that the hinges are too deep inside the door frame. Use cardboard shim to fill the space and then reattach the hinges. Install the door back.
If the doors are painted they can become sticky and they get opened very hard, or closed. Just sand the place and see if this solves the problem. If it doesn’t then use some paint remover and attempt to remove some of the paint. Remove the door if the place is hard to reach. Then repaint the place but with a thin layer. Let the paint dry and reinstall the door.
Sticky interior latches
Sometimes the interior latches tend to stick. Use a pencil and mark the position of the bolt. Close the door and then open it. Look if there are any pencil marks on the jamb. If the bolt isn’t reaching the jamb than you may have an alignment problem of the strike plate. Another problem that may appear is that the strike plate is positioned too far back. Stack a few shims to bring the strike plate out so that it will catch the bolt.