air-quality
The door to a bedroom is closed 24/7. Someone told me, "Be careful. It sounds like you are pressurizing the room."
The room is fairly pressurized, I suppose; I can feel air rushing out from underneath the bottom of the door if I stand outside the room and in front of the closed door.
But what is bad about that? I don't understand the practical significance of air pressure.
Smells don't just appear out of nowhere. Something in your room is the source of the smell (dirty laundry, rotten food, etc). Find the source and remove it. If you can't identify it (too used to it?), then ask your parents to look for it.
If the smell seems to be everywhere in the room, consider deep-cleaning the carpets. (Buy/Rent a cleaner, or have a cleaning service come in.)
If you can't remove the source, all you can do is mitigate.
Leave the door to your room open to avoid stagnant air. Even if something is only mildly stinky, if you leave it in a sealed off room, the smell will permeate the room.
Consider getting an Air Purifier, which will churn the air in your room and filter it a bit. Make sure you stay on top of cleaning/replacing the filter in the unit.
If the smell is a musty/humid smell, consider a Dehumidifier. You will need to empty the drain pan periodically, or attach a drain line to your plumbing. You can also use Damp Rid.
Also, consider that the source of the smell may be you. Your parents may be trying to politely tell you something. Do you bathe every day? Do you wash your hair regularly (at least once every 2-3 days)? Do you put on a fresh change of clothes every day? Do you wear antiperspirant/deodorant? If you answer "no" to any of the above, it may be time to re-visit your hygiene.
Yes, adding a transfer grille or jump duct will be the easiest and most effective solution. It can be done in a way to minimize transfer of sound between rooms (see links below). Adding a return to the master bedroom doesn't guarantee that the supply/return to the master bedroom will become balanced—the resulting pressure may still be positive or even negative with respect to the rest of the house.
Best Answer
In a properly configured home, the return air ducting is the exit path for airflow. There's no significant pressure buildup in any room regardless of door position.
In older homes without return ducting, or vents solely in common areas, the return air path is indeed through or around the door. Still, pressure buildup is extremely small unless the door is extraordinarily well sealed.
You should probably ask "someone" what his or her concern actually is. The pressure differential in your situation is miniscule--probably not even enough to pop your ears. The only downside I can come up with is the accumulation of dust bunnies outside your door.