After a while itll cling to every porous thing it comes in contact with. If you are intent on smokin in yer room use a fan, sit next to it and make sure there is no blow back. A round fan blows back. And make sure you have adequate intake airflow so if you have a fan dont towell the door or youll have more air trying to go out than comes in to replace it and blowback will occurr at the window.
Blow out slow and steady too.
I learned through trial and error when I was in that situation.
Also be wary of the direction of the airflow outside because all the precautions in the world wont help if its just blowin back into your parents room.

Always safest to just go for a stroll, walk the dog.