Steel rusts.

Carbon steel rusts more than just about any other steel.

Motor cars rust, railway track rust, many bridges rust and these are made from carbon steels.

It is a chemical reaction. if you put steel in the atmosphere unprotected it will rust. Steel will if it comes in contact with water, moisture or humidity, turn to a red rust colour. If left, the rust will erode into the metal leaving an indentation or even a hole. On thin very fine edges of steel, the chemical rusting process can destroy the edge beyond repair very very quickly.

Stainless steel is much less likely to rust than carbon steel.

In your situation, I would recommend buying a stainless steel razor because it will be unlikely to rust as long as you dry it carefully before storing it between uses. It is the reason why they made the stainless straight razor.