My neighbours spaniel keeps scratching one of her ears. There is no wax in it and no sign of redness. There are some fine hairs which could be tickling, but surely then she would be scratching both ears? My dogs have never had any ear problems so don't know much about ears. Any advice?

It seems like whenever I simply provide an answer to a question, someone gets upset over it, so understand that I am not telling anyone to delay from seeing a vet, or offering a diagnosis of any kind. Here, I am simply providing information to a question. I recommend the dog be seen by a licensed veterinarian in your area to truly diagnose the problem.

Ok. Now that we've got that out of the way, here are some likely causes of ear problems and/or infections in dogs:
Allergies such as atopy(inhaled) or food allergies
Parasites -such as ear mites
Microorganisms - bacteria, yeast, fungal
Foreign bodies- (something in the ear that shouldn't be)
Trauma
Hormonal abnormalities-ie hypothyroidism
The ear environment- i.e. too much moisture (common in floppy-eared breeds)
Hereditary or immune conditions and tumors

There are many things that can cause a dog to scratch at its ears, so it's best to have it seen by a veterinarian right away to avoid deeper infection. Many times, a simple ointment and regular cleaning of the ear canal is not enough to eliminate the problem, antibiotics may be required in addition. If infection, etc. has been ruled out by a vet, a quality ear cleaning solution for dogs used properly may help. Also, in breeds such as spaniels with floppy ears, less air flow or excessive hair in the ear area can be the culprit. Ask your veterinarian or groomer to show you how to safely and correctly pluck the excessive hair growth. A dog's ears should be inspected regularly. If you notice buildup, wax, redness, or an odor, these are sure signs of an infection and need to be treated immediately.