Hi All

Recently whenever I turn on the AC a really bad smell comes through the vents for about 4-5mins before either I get used to it (urgh ) or it disappears.
It smells like dried kids spew...
I don't have young kids so can't put it down to why it's so bad.
In previous cars you may get a minor smell for a few minutes, but that was more like stale air rather than spew!

Any suggestions, things to check?