Hello, my name is***** and I have over 20 years of experience as a veterinarian. I am very sorry to hear about your kitty's ears breaking out in crusty bumps.
Ear lumps and crusts can also be caused by a food allergy, mosquito bite hypersensitivity, flea bite allergy, a bacterial or fungal ear infection or a particular type of mite called Demodex gatoi which, unlike regular demodex, lives on the surface of the skin, is contagious to other cats, and makes them quite itchy, or an autoimmune (body attacks itself) skin disease like pemphigus.
In some white or light colored cats they can actually get sunburned in the summer which leads to crusty, painful, itchy sores on the ears and sometimes the nose. This is called solar dermatitis and this can progress to a type of cancer called squamous cell carcinoma.
If there is no waxy discharge in her ears a bacterial or fungal infection is less likely as are ear mites.
If this were a food allergy I would expect her to be affected year round, not just in the warm months, unless she eats something different in the summer. Has this been a consistent all year thing?
It is possible that this is autoimmune disease so if this isn't clearing then she should have one of the lesions biopsied.
If this has only become a problem in the last few months then a seasonal problem like mosquito bite hypersensitivity, sunburn, fleas or demodex mites are the most likely causes.
This is a picture of a cat with mosquito bite hypersensitivity. Though it is on the nose in this cat the ears would have similar lesions:
This is a picture of a cat with solar dermatitis (sunburn) of his ears:
I do recommend a quality flea prevention such as Frontline Plus or Advantage II. These are safe and effective, unfortunately they don't repel mosquitos very well. You might try a new product which is a flea collar called Seresto. It contains flumethrin which has shown some mosquito repellent efficacy so I believe it is worth trying. It is expensive but it remains effective for 8 months. Do not use over the counter products as many are not effective and some are even toxic to cats.
To get her some relief if you think that her lesions are getting itchy you can try antihistamines, either:
1) Benadryl (diphenhydramine only, the combination products with decongestants and acetaminophen are toxic to cats) at 1mg to 2mg per pound of body weight every 8 to 12 hours. That's a half of 25mg tablet every 8 hours for a cat that is 8 to 15 pounds.
2) Chlorpheniramine at 4mg once or twice daily per cat.
3) Zyrtec (Cetirizine hydrochloride) at a dose of 5 mg per cat given orally every 24 hours. (Make sure it is NOT the formulation with a decongestant (such as Zyrtec-D) because cats cannot tolerate decongestants.)
Side effects of antihistamine use are drowsiness and dry mouth.
I would also recommend an omega 3 fatty acid supplement. These are natural anti-inflammatories and work synergistically with antihistamines to relieve the itch. They are also good for coat and skin health in general. My favorites are 3V Caps and Derm Caps as they are formulated for pets and are high quality products. I recommend an omega 3 fatty acid dose based upon the EPA portion (eicosapentanoic acid) of the supplement, as if we do that the rest of the supplement will be properly balanced. Give him 20mg of EPA per pound of body weight per day. For example an 8 pound cat could take 160mg of EPA per day. Together antihistamines and omega-3 fatty acids work synergistically to relieve allergy symptoms.
You can also apply a little cortisone ointment to her ears (like Cortaid) once or twice daily.
You can also try puncturing a vitamin E capsule and applying that to the lesions on her ears.
Just in case this is mosquito bite hypersensitivity or sunburn I recommend keeping her indoors, or at least on a screened porch if you have one, until her ears are healed. It is especially important that she be kept in during prime UV ray time, between 10 am and 3 pm and at dusk and dawn when mosquitoes are most active. When she does go outside during daylight apply a baby safe sunscreen to her ears.
Please let me know if you have any further questions.