There are more than just A320 APUs that create contaminated air into the bleed air and packs if started and immediately have the bleed/packs switched on.
The A330, 340 and 380 that I have flown, will also generate the smell of sweaty socks or smelly running shoes through the air conditioning and this is the definitive symptoms of oil leaking into the compressor section through the labyrinth seals and being heated and turned into the accumulative toxin in the oil fumes. Moving Jet II oil is the problem due to its additives.
So the big picture is your health danger of the accumulation of these oil fumes over a long career, known as Aerotoxic syndrome, google it. My specialist told me 60% of people are unable to detoxify this synthetic oil fumes toxin.
All pilots should learn early what the oil fumes smell is like and take whatever steps to avoid it including delaying Packs on in this procedure and encouraging your company to adopt oil fumes mitigation safety over absolute minimum time from APU start to packs on.
I am an oil fumes incident survived and urge you to take it seriously.