In general, steel, including tool steel, will rust if it is given the opportunity to do so.
First of all, this requires the presence of oxygen and water, both of which are contained in the air. If the humidity condenses on the tool due to temperature fluctuations, rust can occur.
For this reason, we oil our pliers before they leave our factory, but the oil film wears off with use.
For the preservation of the surface against rust, basically all commercial preservation oils can be used without hesitation. When selecting an oil, we recommend a clear spray oil that is not too greasy.
To remove rust from your pliers, you can work on them with an abrasive rubber, for example, and then oil them.