Can my apartment become moldy if I don't live in it? I don't understand the whole negative air pressure thing
Is it bad if my apartment doesn't get any drafts in it? I want to block the front door gap, but my dad got mad and said this would cause mold issues.
How and why? I mean I don't live there so why would it become humid?
It's not really an option to keep it open cause I'm allergic to some of the stuff that comes in from the neighbours
Follow up question: is it true that turning the bathroom fan on won't do anything, if there isn't somewhere outside the apartment that air can be drawn from?
Apartments and houses are designed for air flow. You don't need a gap in your door to prevent mold. Mold will grow despite that if you live in a city that has high humidity.
Everyone should watch for mold. Check around windows. Behind the toilet tank. Above and around the shower. Wipe with bleach often.
You can also get a dehumidifier if it becomes a problem
I would get a dehumidifier before resorting to wiping with bleach often. If you ever see mold, you already have a humidity problem. This may be isolated to your bathroom due to extra moisture from showers, but it's still a problem that needs to be addressed. If it's just the bathroom, a new shower fan (or just using the existing one) could be enough.
I don't understand what you mean when you say you "don't live there" ?
Regardless, if you consider mold in general then the room which most typically gets mild growing is the bathroom, because it's moist and warm which is perfect condition.
It doesn't take much to get mild growing in other places too though. If you have moisture in the air then mould could happen.
Good ventilation helps prevent mould because it lets the humid air created from normal activities like cooking and washing escape and be replaced with drier air from outside - assuming you live in a climate that doesn't have crazy humidity.