Keeping cats in apartments can indeed produce some odor, but the extent depends on how the cat is cared for and hygiene habits. To reduce odor, the following measures can be taken:

1. Clean the cat litter box daily to reduce odor.
2: There are various deodorizers and air fresheners on the market that can help remove odors.
3. Regularly opening windows for ventilation helps to dissipate indoor odors.
4. Regularly bathe and groom your cat to keep it clean.
The above measures can effectively reduce the odor caused by cats in apartment buildings.