Why do I see fog in my refrigerator when I open its doors?

This is not unusual.

When the refrigerator doors are opened, the hot and humid air outside the appliance meets the colder and drier air inside. This causes water vapor from the warmer air outside to condense and take on a fog-like form. This is especially the case in warmer temperatures or climates. 

The amount of fog might increase if appliance's doors are opened too often or left open for too long. Make sure food or other items are not obstructing the doors from being closed.

Check the door seals to see if there are any gaps between them and the cabinet. If you find any, adjust the door seal by gently pulling it away from the door using your fingers. If the doors are not sealing properly, try cleaning the seal with a soft cloth or sponge and warm water. Avoid using abrasive cleaning products as they might damage the seals.

If a seal is loose or cracked, it needs to be repaired or completely replaced. If you suspect this to be the case contact an authorised service agent.