I apologize that for some reason our communications were not working well yesterday, I know the website was experiencing some issues. Unfortunately I had signed out before your last replies so I am just now seeing them. I am going to copy and paste all my previous responses below again to be sure you see them:
Ok. The spot on her neck you took an image of looks like it could be a benign sebaceous growth- it is hard to tell without being able to see it in person, but if it is small and not red or irritated, I would continue to monitor it for changes and let your vet know about it next time they see her (or take her to have it looked at earlier if it is changing at all).What you are describing (patches of hair loss with red skin with small bumps) most commonly is the result of an allergy. We can have allergies develop later in life, so just because she hasn't had any issues previously doesn't mean this isn't allergy related. We can have allergies to things in the environment (called Atopy) like grasses, pollen, trees, dust. We can also develop allergies to food ingredients (most often a protein). Many dogs just get mild allergies which can be controlled with antihistamines and fatty acid supplements and just get flare ups occasionally. For more severe allergy cases we need to be more aggressive by doing things like prescription diet trials or allergy testing, or stronger drugs. Sometimes as a result of allergies we can get secondary skin infections that require antibiotics to treat them.... It is possible she may respond to an at-home treatment, but sometimes these guys do need a short course of steroids to get the itching cycle under control, and sometimes they do end up needing antibiotics for secondary infections.So the safest thing is always to have your dog examined by your vet, or to discuss any medications (even over the counter) with them prior to starting, since they know your pet's health history and can determine what is appropriate for your individual pet. There are some over the counter options that can be effective in mild allergy cases. These would include a fatty acid supplement (you can find these at most pet stores or at your vet's office as a capsule or a liquid to place on their food). An antihistamine can also be helpful in milder cases. The most common one we start with over the counter is diphenhydramine (benadryl). You have to be careful you get plain diphenhydramine- no other added ingredients (some products also contain tylenol, etc.). Here is an article on diphenhydramine, its side effects/precautions/doses:http://www.petplace.com/article/drug-library/library/over-the-counter/diphenhydramine-benadrylThe other thing you can try is a topical hydrocortisone- you can get a spray like Cortaid spray, or a topical ointment to apply to the areas 2-3 times a day. The issue is if she is licking/biting her hind quarters it isn't going to stay on her skin long (that is why the oral steroid can be helpful in stopping the itch much faster).Any worsening- increased hair loss, more bumps appearing, oozing of the skin, bumps that look like whitehead pimples, circles of dry/dead skin appearing, these would all be signs of a secondary infection that will require a prescription from your vet.As far as mites, the more common mites we see in pets (demodex, sarcoptes, cheylietella) are species specific, so it is always possible with skin issues we could have mites, but what you are describing sounds more like allergies and if it was mites, it wouldn't likely be affecting both the dog and the cat. Fleas, however, can, and if you just recently started them on flea preventative, it is possible this is a reaction to flea bites they had previously. Also, you are correct in that some pets are extra sensitive to flea bites and just one bite can trigger a bad skin reaction. It is great you have them on flea preventatives, but it doesn't gaurantee they will never ever be bitten by a flea so that is a possibility. Please let me know if you have any other questions and if my response came through to you!!!