Thank you for your patience. There are a number of possible causes for Javier's itchiness in this area. Firstly - you need to make sure that Javier is definitely up to date with flea control. Make sure you are using a flea product appropriate for his weight. Even if you cannot see any fleas on him doesn't mean there are one or two lurking and oftentimes this is all it takes for a dog with flea allergy dermatitis. In your boy's case it does sounds like he may have an underlying allergy of some sort with secondary infection, however this could also be caused by parasites or fungi (ringworm or yeast).
Bascially dogs are allergic to four main things - food, fleas, grasses/plants (contact allergy) or environmental allergens (canine atopy - the dog version of ezcema). Flea allergies are avoided by strict flea control - every 4 weeks with Advantage or Advocate or every 5 - 6 weeks with Frontline. You must also ensure any other cats or dogs in the household are treated at the same time. I would also recommend that you wash all of Javier's bedding, and also consider a flea bomb of the house (although be sure to get all pets and humans out of the property for this - depending on the product you use).
Contact allergies are best treated by avoidance of the plants that are to blame, but identifying the exact cause of a contact allergy can be very hard. A referral to a canine skin specialist may be the way to go in Javier's case for either a skin patch test or a blood allergen test. If you have recently moved house in the last year, or if you are taking Javier for a walk in a new area, then his symptoms could certainly be due to an allergy to one of the grasses or plants he is coming in to contact with. If you take him for walks in grass that touches his belly - try avoiding this area for 2 - 3 weeks to see if that effects his symptoms.
As for the potential for a food allergy - we certainly also have to consider this. Dogs can become allergic to certain proteins in food, and if you have changed Javier's diet at all, or introduced a new treat in the last year, then we certainly have to consider this. If this is the case for your boy, I would recommend carrying out a full diet trial with a hydrolysed protein diet like Royal Canin Anallergenic or Hill's Z/D. Your Vet can help with this - but Javier won't be allowed any other food, snacks, treats or tidbits during this 8 - 12 week trial.
It is also possible that your boy may even have skin mites or lice. These could be either Demodex (less itchy) or Sarcoptes mites (VERY itchy) and you should ensure a full Veterinary check up so that he or she can carry out a physical examination and possibly a skin scrape to check for mites and lice, as well as signs of fleas.
You should also continue to use the medicated shampoo that will deal with both yeast and bacteria, and the product Malaseb is the most ideally suited for this. This requires you to make a lather and leave this lather on for 10 minutes before washing off! For many clients this is easier said that done, but it is SO important. This shampoo helps to deal with any secondary infections and will potentially be important ongoing for your boy depending on the underlying cause of his itching. Sometimes steroids are necessary as well, but the less the better. There is a fantastic new product that appears to have less side effects than steroids, called Apoquel, and your vet can help with getting your boy on this as well potentially.
Best of luck with Javier and do follow up on some of the above with your vet. In the meantime, make sure he is up to date with his flea treatments, and make sure the house and his bedding are flea-free. I hope all of the above makes sense? If you have more questions or if I can help in any other way, please do not hesitate to ask! If you would like to accept my answer, please press RATE OUR CONVERSATION (I am not compensated in any other way). Bonuses are always welcome. Thanks! I hope to work with you again soon!
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