Condensation or fogging on the inside of the glass door.

This is usually not dangerous but can indicate a sealing issue.

• Check gasket seal: Close the door on a thin piece of paper at several points around the frame. If the paper pulls out easily, the gasket may not be sealing.
• Reduce openings: Limit how often and how long the door is opened, especially in humid environments.
• Ventilation: Improve room ventilation or use a dehumidifier if the room is very humid.
• Door heater (if present): Some models have a low-wattage heater around the door frame. If the frame feels cold and condensation is heavy, the heater circuit may have failed and should be checked by a technician.

Replacing a worn gasket often significantly reduces condensation.