This is not dirt or mould.
This is leaching plasticizer....a sign that the plastic is breaking down.
Degrading plastics can get sticky, they can get coated in a variety of weird substances and they can get a funky smell.
Degrading plastics can become brittle and fragile.
The degradation process can not be stopped.
I can clean the leached plasticizer off your doll but I cannot tell you how long it will last.
So your doll can go from this:
To this:
But I cannot tell you how long the cleaning will last. The plasticizer will reappear at some point. It might be 1 year, 10 years...who knows.
If you keep the doll away from extreme temperatures and humidity, it will slow the degradation process down. It is also important to keep the doll away from other vintage plastics as some degradation processes produce gasses which will adversely affect other plastics.
The degradation process can not be stopped.
I can clean the leached plasticizer off your doll but I cannot tell you how long it will last.
So your doll can go from this:
To this:
But I cannot tell you how long the cleaning will last. The plasticizer will reappear at some point. It might be 1 year, 10 years...who knows.
If you keep the doll away from extreme temperatures and humidity, it will slow the degradation process down. It is also important to keep the doll away from other vintage plastics as some degradation processes produce gasses which will adversely affect other plastics.