Why are my nails so despicably filthy?

[TheDevilWearsPrimark]

I keep them quit short (4mm, yes I have just checked with a ruler)and file and buff them regularly. I am quite blessed wih very white tips and hate nail varnish.
But despite the amount of washing up and handwashing I do they seem to be dirt magnets. I am often embarrassed when gesticulating and realise my fingernails are full of crud.

How do I stop this and why does it happen?

depends on the shape of your fingers

I find vigorous hairwashing cleans them quite well, otherwise I use a nailbrush

I'm mucky too.

Rouge Noir.

I use a nail brush but I immediately get dirty again.

I clearly have dirt-magnet shaped nails, because mins are closer to 1mm and accumulate muck within minutes.