House doesn't smell fresh. Ever.

[retreatingheadlights]

I clean my mum's bungalow top to bottom weekly and hoover most days. It never smells fresh when I walk in. There's an odour that I can't put my finger on. Like unwashed clothes or bedding except they are washed regularly. I change the bed every other week as there's only mum in it. The duvet is a couple of years old and looks new. New pillows. Mum showers every other day and washes her hair. The rubbish is put out every day that I'm here which is 4-5 days a week. She's not incontinent. It's a little bit old person house smell but not quite.
I've put Zoflora on the radiators this morning and did it at the beginning of the week too. It's not the drains. It's not the carpets and the windows are opened daily.
It's driving us mad and upsetting mum that her house smells.
Any ideas what it could be and how to fix it?

If any of the washing wasn't quite dry you would get that smell, is usually damp from somewhere or another

It’s supposed to start around 40.. gradually gets stronger. In Japan they use Persimmon soap, but eating mushrooms also gets rid of the smell as it’s a chemical people produce more of as they age, something in mushrooms stops it.