my shar pei has developed a sore patch on his shoulder area

Hello, I'm Dr. Kara and I have over 20 years of experience as a veterinarian. I'd like to help with your concerns about Jairo's red, moist, sore spot on his shoulder.

This sounds like a hot spot or an area of superficial skin infection.
Hot spots are caused by the skin getting wet, sometimes from swimming or bathing and not getting dried off properly but most of the time they come from a dog licking, chewing or scratching an itchy area and breaking the skin barrier, allowing bacteria that normally live on the skin to get in the skin and thrive. That can be from an insect bite or sting or an allergic reaction.

If this is a hot spot then getting him to stop licking and scratching and allowing the skin to heal will help resolve it. This likely involves placing an elizabethan collar so he cannot reach the area and treating the underlying allergy.

Allergies are the most common cause of itchy skin. I'll give you an allergy rundown of likely causes for skin troubles. He may have more than one allergy given how symptomatic he is now. Dogs that have one allergy often develop several with time. The effect of multiple allergies aren't additive, they actually compound one another.

Even if you don't see fleas I do recommend using protection. They are the most common allergen and it only takes one bite a month to make an allergic dog scratch so I recommend using flea prevention even if you never see one again. Frontline Plus , Advantage II or Advantix are excellent. Don't use over the counter products, especially Hartz or Sargents, as most are ineffective if not toxic.

Other allergens can be inhaled (like grass pollen, dust mites or molds) and you can use a combination of antihistamines and high doses of omega-3 fatty acids to help control his reaction to those (they also help with the symptoms of flea allergy). In combination fatty acids and antihistamines work synergistically, much better than either one alone. If his symptoms worsen seasonally I would think that inhaled allergens are a part of his problem.

You can try:
1) Benadryl (diphenhydramine only don't use the combination products with acetaminophen or decongestants as they can be toxic to dogs) at 0.5mg to 1mg per kilogram of body weight or one 25mg capsule per 8 to 12 kilograms of body weight orally every 8 hours.
OR 2)Claritin (loratidine) at 5mg per 12 kilogram dog once or twice daily.
OR 3)Hydroxyzine at 0.5mg per kilogram of body weight orally every 8 hours.
OR 4) Chlorpheniramine at 4mg to 8mg per dog once or twice daily.
Some dogs do better on one antihistamine rather than another.
Give the one you pick a 5 to 7 day trial and if it isn't working try another. Be aware that antihistamines can cause sleepiness or hyperactivity in some dogs. These side effects do wear off with repeated use.
Omega-3 fatty acids are fish oil products. 3V by DVM or Derm Caps ES are good brand name products. Use the high end of the dosing schedule for your pup's weight. 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 to 40mg of EPA per kilogram of body weight per day. For example a 20 kilogram dog could take 400mg to 800mg of EPA per day.

Clip a wide area around and over the hot spot lesion very short and use a solution mix of Betadine solution (povidine iodine solution) and warm water, made to look like weak tea, and clean the affected area twice daily. This is an antibacterial and will dry the lesion out to allow it to heal. There is no need to rinse it off, just clean the lesion several times and then leave on to dry. It does stain horribly though so you probably want to do this outside. You can find this at the drug store over the counter.

In some cases if the lesion is quite deep he may need oral antibiotics too, so if he isn't much better in 48 to 72 hours then he may need to see his veterinarian.
Please let me know if you have any further questions.

Thank you for the further information. I am very glad to hear that he is already protected from fleas.
I am also pleased to hear that he isn't bothering the spot. It may be too sore to touch by this point if it looks raw. Seawater is contaminated water and can be a skin irritant. I recommend owners rinse their pups with fresh water after a swim to ease the irritation.
I would recommend clipping his hair in the area and in a wide margin around the spot to get air to his skin and clean it to remove the bacteria and the oozing coming from his raw skin. These infections spread quickly if we don't get ahead of them and dried out.