Why can’t my vet just look at my cat’s skin and tell me what’s wrong?

Because a huge range of very different problems, food allergies, flea allergies, environmental allergies, fungal infections, bacterial infections and nutritional gaps, can all produce the same surface symptoms: itching, hair loss, small scabby bumps. Two cats with identical-looking patches on their neck can have completely different causes and need completely different treatment. That overlap is exactly why a vet often needs skin scrapes, bloodwork or an allergy trial rather than a diagnosis from a glance, even for an experienced eye. It is not extra caution for no reason, it is the only way to actually tell the causes apart.