My name is ***** ***** I’ve been involved professionally with dogs in the health and behavioral fields for over 18 years. It will be my pleasure to work with you today.
It sounds like he may be having an allergic reaction to something. I would necessarily say it pointed to the dewormer as an allergic reaction can be triggered by almost anything such as cleaning supplies or even grass. Check his food to be sure they haven't changed formulas. They often do without any notice such as new or improved. You can read up on allergies here:
It could even be a new treat. If you think the food may have changed, you could do a food trial and use the elimination method described on the following website.
Check to see if any yard treatments were used or think about a change in laundry detergent or carpet cleaner or deodorizer. Some older dogs even develop allergies to things that they previously tolerated. It may take several weeks to see improvement after you eliminate the allergen. You may also give your dog Benadryl up to 2mg per pound every 8 hours and if you see improvement, that might indicate an allergy reaction was the cause.
There might be a secondary skin condition in addition to the allergy such as staph dermatitis or yeast dermatitis. Staph usually occurs on the lower regions of your pet and tends to have small pimple type bumps. Shampoo containing Chlorhexiderm and/or Oatmeal can help with this condition though it does not cure the allergy. Yeast typically shows as a greasy area that has a sweet musty odor. Sometimes the skin can become inflamed, darker and thickened due to itching. Yeast likes areas such as between toes, armpits and ears. Selsun Blue Shampoo can help with Yeast dermatitis. When shampooing, lather and leave on 15 minutes before rinsing. These shampoos are not meant to be a cure, just a relief until your pet can see a Vet.
I hope this information is helpful to you. If you would like any additional information or have more questions please don’t hesitate to press the reply to expert or continue conversation button so I can address any issues you still have . If you do find this helpful, please take this opportunity to rate my answer positively so I am compensated for my time.