There may be several reasons why the cat’s hair is not dry after external deworming. First of all, deworming drugs may remain on the cat’s hair, making it difficult for the hair to dry out. Secondly, if too much anti-parasitic drugs are used, the cat's hair may be too wet and difficult to dry. In addition, if the quality of deworming medicine is poor, it may also cause the cat's hair to be difficult to dry.

In order to solve this problem, you can try the following methods:

1. Make sure the deworming medication you use is of good quality and avoid using too much. 2. After using deworming medication, you can use a hair dryer to gently dry the cat's hair. 3. If the cat’s hair is still not dry, consider changing the brand or type of deworming medication. It should be noted that although the above methods can help solve the problem of cats’ hair not drying after external deworming, it is recommended to consult a veterinarian if the problem persists.