Even if a cat doesn't have worms, it still needs deworming because deworming is preventative and needs to be done regularly. Deworming only occurs when parasites are present, and that's considered therapeutic deworming. Too many parasites can lead to various secondary diseases. Cats generally need external deworming about once a month and internal deworming about once every three months. Also, avoid using the same deworming medication for extended periods. 
Symptoms of parasite infection in cats:
1. Frequent vomiting: If a cat is infected with parasites, it will experience symptoms such as nausea and vomiting.
2. Physical discomfort, excessive hair loss, and susceptibility to skin diseases.
3. Abnormally high body temperature or hot ears.
4. Pale gums, anemia, or blood in the stool.
5. Having large red rashes on the skin or frequently licking or biting certain parts of the body, such as the buttocks.
6. There are foreign objects in the excrement.
