If your cat's neck has a spot that's been irritated for about a month and has gotten larger from scratching, it’s a good idea to take them to the vet for a proper diagnosis. Skin issues can be caused by a variety of factors, including allergies, parasites, infections, or even stress, and scratching can make things worse or introduce infection.
In the meantime, you can try to discourage scratching by covering the area with a soft cone collar, which can help prevent further irritation. However, home remedies may not fully address the underlying issue, and some treatments might even make it worse if the exact cause isn’t known. The vet can provide the best guidance, potentially prescribe a topical treatment, or suggest ways to prevent it from spreading or becoming infected.