Stainless steel is generally not microwave safe because it reflects microwaves, which can cause sparks, arcing, uneven heating, and potentially damage the microwave or create a fire hazard. However, some specially designed stainless steel containers with smooth, rounded shapes and microwave-safe labels exist that avoid sparking and are deemed safe for microwave use under specific conditions. These containers are made to withstand microwave heating without causing dangerous effects. Key points about stainless steel in microwaves:

• Regular stainless steel containers are unsafe as they reflect microwaves and can generate sparks or arcing.
• Microwave-safe stainless steel containers are designed to prevent these risks, often with rounded edges and special manufacturing.
• It is crucial to avoid damaged stainless steel containers and never run a microwave with empty stainless steel inside.
• Even microwave-safe stainless steel should be used with caution, following manufacturer guidelines, limiting heating time, and ensuring the container does not touch the microwave's walls.

Overall, unless explicitly labeled as microwave safe and designed for it, stainless steel should not be used in microwaves. Safe alternatives include glass, ceramic, or certified microwave-safe plastics for reheating food.