Is there green corrosion in the hearing aid as well?
My guess is sweating has caused this.
Use compressed air to blow out what you can. A tiny bit of dielectric grease on the connection might stop the problem.
Yes, I checked the other part of the hearing aids. No noticeable green stuff.
I try to brush it hard, try to blow it out or try to suck it out. It stuck in a tiny hole in the connector for good.
What concerns me is, whether green corrosion will spread if other metals come into contact with it? like bacteria spreading if you touch it or something.
I checked the receiver, it working fine. The best I can do is buy a new one and don’t think about it but that would be a waste of money.
Corrosion like that on electrical connections in general is not good for a circuit and will only get worse if not removed. It will not be easy to remove without some way of physically scraping the surface.
Sweat (moisture) react with copper likely to give a green coloration. It looks like an oxidation has occured - sweat + copper. Used a dryer every night if possible.
Get a spare one just in case there is a problem.