Why can we smell our neighbors cooking upstairs?

[Stuckforthefourthtime]

Ever since moving in, we've been able to smell our neighbours' cooking in our 1st floor bathroom (adjacent to their wall) - but now all our upstairs bedrooms including the loft are filled with the smell of their dinner every night. It's not great!

We get on well, so will discuss this with them directly, but would like to have an idea of what might be causing it first.

If relevant, we share a chimney stack and have both had lofts put in around the time of moving, plus they moved their 1st floor bathroom (used to adjoin ours, now that's a bedroom).

And apologies for poor grammar at top!

Do you have your windows open?

@NotSuchASmugMarriedNow1 nope - and nor do they.

Could they have installed an over-cooker extractor hood, that sucks the air through filters, but is not vented to the outside?

I moved into a house where such a system efficiently reduced cooking smells from kitchen, and, because of the way it had been installed, delivered them to the bedrooms above.