Skin disease in cats is most frequently due to fleas, even if they are not always seen.
If a cat continues to scratch, overgroom or lose hair once a comprehensive flea control program has been established, there may be other underlying reasons for this.
Anxiety, food allergies, mites and atopy are amongst the other causes for this and investigation should be methodical and can sometimes be prolonged.
As with humans, itchiness is a source of discomfort and so advice should be sought to relieve the irritation. We can then carry out a thorough examination of the patient and discuss treatment options and investigations as necessary.
The following link from International Cat Care Organisation gives further information: https://icatcare.org/advice/the-pruritic-itchy-cat-when-it-is-not-fleas/