Can smell the person upstairs using bathroom?

So I just moved into a new place (this one is five or seven years newer than the place I was living before) and I noticed that sometimes in the mornings (only the morning) the bathroom would stink, something that my old place didn't do.

It wasn't like a rotting kind of stink, but the kind of stink that you find after your boyfriend has been pooping in the bathroom for 15 or so minutes without the fan on after eating garlic and onions the night before. Or something like that.

Anyways, I thought that it was stuck water at first, but after cleaning the drains and making sure that there wasn't anything that would even produce that smell in that area, I was left to assume that it was some sort of phantom smell that Japanese bathrooms produced.

It wasn't until I was doing my business in the bathroom when I heard the upstairs (i'm pretty sure upstairs) neighbor's door shut, and then after perhaps 15 seconds it started to produce that terrible smell again.

Is it at all possible to find something to stop my neighbor's smell from leaking into my apartment? Or am I just going to have to hopelessly suffer for the next few years while I live here?

Any advice at all is appreciated, seriously.

I actually had a similar problem a few years ago at what was a relatively new apartment.

It turned out, upon inspection, that the company who had built the apartment had forgotten to put a seal over a connection between the water heater and the main pipeline.

So, basically, the scent of raw sewage was filtering into my apartment, day after day. :/

I'd immediately suspect something similar at your place.

If you can speak Japanese enough to explain the problem, or you have a Japanese friend who can, I'd suggest calling your landlord about the issue.

Is it a wooden "apaato," or is it (usually) reinforced concrete "manshon" type of building?

If it is an old wooden structure, then the upstairs' floorboard might be just not "airtight," so that the odor just leaks through. If that is the case, hope that they start opening the window to ventilate the bathroom better. If it is a concrete building, then something is wrong with the pipes (maybe there is some bend in the pipe where water stagnates).

Thank you so much for your answers so far!!

The apartment is (supposedly) a reinforced concrete mansion, so assuming that it actually is then there must be something wrong with the water, right?

I only notice the smell every once and a while, however, so would that still be stagnant water or just my neighbors bathroom smells filtering not outside but into my apartment?

Even the landlord wouldn't know unless they got a plumber or somebody to come have a look. I hope you can talk to the landlord to get them to do that :)

I am not a plumbing expert but I work in construction and know that if vent pipes are clogged it can lead to a back up of smells in a bathroom. The drainage pipes (from tub, sink and toilet) must be vented for several reasons. The vent pipe usually vents to the roof. Calling a plumber to inspect the problem (or having your landlord call a plumber) should be the first step to make sure the vent pipes are free and clear to do their job.

I agree with the last poster. Sounds like backed up sewage gases coming up your drain. I had this problem in the past, especially in summers when the heat would evaporate the water in the floor trap. What solved it for me was to pour water down the drains every so often so they didn't dry out.