What is the most likely diagnosis for a dog with a progressive skin lesion in warm weather?

The diagnosis of atopy, or allergic dermatitis, is the most likely for a dog exhibiting progressive skin lesions in warm weather. This condition is often triggered by environmental allergens that are more prevalent during warmer months, such as pollen, mold, and dust mites. The symptoms typically include itching, redness, and a progression of skin lesions as the dog continues to be exposed to allergens.

In warm seasons, the increased presence of pollen can provoke an immune response in susceptible dogs, leading to the hallmark signs of atopy. The lesions may appear on areas such as the paws, face, and belly, where the dog is more likely to come into contact with allergens.

While other conditions like dermatophytosis, or fungal infections, can also cause skin lesions, they are not specifically associated with seasonal changes in the same way atopy is. Hypothyroidism generally causes non-specific scaling, hair loss, and lethargy rather than progressive lesions influenced by environmental factors. Similarly, hyperadrenocorticism leads to a different set of skin signs, such as thinning of the skin and increased susceptibility to infections, rather than a progression of lesions in response to heat or allergens. Thus, the characteristics and timing align more closely with atopy as the primary