Stainless steel does not rely solely on its surface to resist rust; instead, it prevents further oxidation through the formation of a chromium-rich oxide layer. This very thin yet strong oxide film on its surface blocks oxygen atoms from penetrating the metal, thus preventing further oxidation. However, if this layer is damaged—such as by scratching or wear—oxygen atoms from the air can infiltrate the metal, causing iron atoms to precipitate and form loose iron oxide, commonly known as rust.

The main reasons for rusting in stainless steel include:

1. Electrochemical Corrosion: If there are dust particles or foreign metal fragments on the surface of stainless steel, in humid air, these contaminants can create a micro-battery with condensed water between them and the stainless steel, triggering an electrochemical reaction that damages the protective film.

2. Organic Corrosion: Organic substances (such as vegetable juices, soup, or saliva) that adhere to the surface of stainless steel can form organic acids in the presence of water and oxygen, leading to corrosion over time.

3. Acidic, Basic, and Saline Corrosion: Substances containing acids, bases, or salts (such as splashes from alkaline water or lime water during construction) on the surface of stainless steel can lead to localized corrosion.

4. Chemical Corrosion: In polluted air (such as environments with high levels of sulfides, carbon oxides, or nitrogen oxides), condensation can lead to the formation of sulfuric acid, nitric acid, or acetic acid droplets, resulting in chemical corrosion.

To prevent rusting in stainless steel, the following measures can be taken:

1. Regular Cleaning: Frequently clean and wipe the surface of stainless steel to remove contaminants and eliminate external factors that can lead to rust.

2. Proper Maintenance: Particularly in coastal areas, stainless steel is less resistant to seawater corrosion, so it's important to develop good usage habits and regularly clean and keep the surface dry.