Ferrets with colds, flu, or other respiratory infections have runny noses that may be completely blocked with discharge. They can neither breathe nor eat when this happens. Wipe the nose with a tissue. If there is a lot more discharge inside, put the ferret in a steamy bathroom or in a small room with a baby vaporizer until the mucous is softened and can be wiped away. Put a small amount of VaselineTM around the nostrils to help prevent the secretion from drying again. Moisten the ferret's regular pellets with water and microwave it to bring out the flavor and odor and tempt him (or her) to eat. Ferrets that refuse to eat even after their noses are cleared, or that have large amounts of thick yellow or green nasal discharge, will probably need antibiotics and should visit a veterinarian.
If your house is very dry, get a humidifier for the ferret's living space. Do not keep him in the warmest area of the house, which will be stressful for him. Keep him in a cool area and provide a warm nest for sleeping. The cage and litter box should be kept extra clean to avoid irritating ammonia fumes. If there is a smoker in the house, the ferret's quarters should be protected from the smoke.