It's normal for cats to occasionally have nasal discharge. Cats produce a small amount of nasal discharge during their metabolism. Owners can wet the cat's nose with water and gently wipe it away with a clean tissue. However, if a cat has persistent nasal discharge, or if the discharge is yellow, purulent, or watery, it indicates that the cat is sick. Owners should observe the cat for any other abnormalities and it is recommended to take the cat to the nearest veterinary hospital for examination immediately. 
Reasons why cats have boogers:
1. Viral or fungal infections: Common viruses and fungi include herpesvirus, calicivirus, Aspergillus, Cryptococcus, etc.
2. Foreign body irritation: Nasal secretions may occur on one side only.
3. Rhinitis: Allergic rhinitis can cause secretions in the nose.
4. Spread of oral diseases, such as root abscess and nasal fistula.
5. Common cold: Increased nasal secretions caused by respiratory infections due to colds.
