Can smoke travel through vents in apartments?

Yes, smoke can definitely spread through the ventilation ducts and other hidden gaps of the apartment to other rooms. This is a very common and troublesome issue.
In simple terms, modern apartments, in order to ensure building safety and energy efficiency, share a series of piping systems. These pipes then become channels for smoke to spread.
The main pathways of smoke transmission
Ventilation ducts in bathrooms and kitchens: This is the most common transmission route. In a building, the exhaust fans in all bathrooms and the range hoods in kitchens are usually connected to the same vertical main exhaust shaft. When a neighbor turns on their exhaust fan, the smoke from their home will be directly drawn into this public duct, and then seep back into your home through the gap of the closed exhaust fan. What you smell is generally the second-hand smoke emitted by your neighbor.
Central air conditioning or fresh air system: If the apartment uses central air conditioning or a unified fresh air system (HVAC), then smoke can easily be drawn in through the return air vents and transported through the pipes to other rooms. In this case, what you might smell could include second-hand smoke, or even the mainstream smoke (the smoke directly exhaled from the mouth) produced by neighbors when they smoke.
The gaps between walls and floors: Even seemingly solid walls and floors actually have many hidden gaps. For example:

Holes for pipes and wires passing through walls: The holes reserved during the installation of pipes and wires. If these holes are not completely sealed with fireproof mud or foam glue, they provide an excellent passage for smoke.
The joints between the floor and the baseboard: These areas may appear sealed, but there are usually tiny gaps that allow odors to seep through.
Outlets and switch panels: The outlets and switches installed on the common wall often have their back covers connected to the cavity inside the wall, forming a smoke passage.
Why do I feel that the smell of smoke is particularly persistent?
Small gaps: The smoke molecules are extremely small and can penetrate tiny gaps that are almost invisible to the naked eye.
Wind pressure effect: When a household opens the exhaust fan or when the wind pressure in the corridor changes, a pressure difference will be formed, pushing the smoke from the high-pressure area to the low-pressure area.
Pipeline "Memory": The smoke oil will adhere to the inner walls of the pipeline. Over time, as it accumulates, the pipeline itself will emit an aged tobacco smell, even without any new smoke being produced.
If you notice smoke flowing back in, what should you do?
If you are bothered by the smell of smoke from your neighbors, you can try the following methods (before renting a house, you can also check if there are relevant clauses in the contract):
Check and seal the gaps:
Check the interfaces of the exhaust fan and the range hood. You can try replacing the exhaust fan or the hood with one that has a backflow prevention valve (also known as a one-way valve). The backflow prevention valve will automatically close when the machine is turned off to prevent backflow.
Check the holes around the water pipes and gas pipes, and seal them with fireproof expanding mud or foam adhesive.
Check the sockets and switch panels. You can purchase socket sealing pads or sealant mud to fill the gaps between the panel and the wall.
Check the joints between the baseboard and the floor and walls, and fill the gaps with transparent sealant or putty.
Change the direction of air flow:
If your home's exhaust fan is constantly running, it might suck in the smoke from the public pipes. Try to turn it off and seal it to create positive pressure.
In rooms with less pollution, you can open the windows to ventilate, creating a positive pressure that will push the air out of the room and prevent smoke from the corridors or pipes from entering.
Using an air purifier equipped with HEPA filter and activated carbon filter can effectively filter out the smoke particles and odors in the air.
Communicate with neighbors and the property management:
You can first communicate politely with your neighbors. In many cases, the other party may not be aware of the problem.
If communication fails, you can report it to the property management or the homeowners' committee. They can check if there is any gas leakage in the public pipes, or coordinate according to the provisions of the Civil Code regarding adjacent rights. According to the law, neighbors are not allowed to discharge "pollutants" that cause harm to others.
Consider legal means: If the problem is serious and cannot be resolved through negotiation, you can consult a lawyer, collect evidence (such as videos, witnesses, air quality test reports), and use the legal process to protect your rights. However, this step is costly and is usually the last resort.
?? Summary
Smoke spreading throughout the apartment through ventilation ducts and building gaps is a common phenomenon. The key to solving this problem lies in two points: First, sealing the gaps in your own home, which is something you can control completely; second, collaborating with neighbors or the property management to address the issues with public ducts or the source.
I hope these details will help you better understand the problem. If you need to know more specific methods for blocking, such as how to use foam glue, please feel free to ask me anytime!