Does your dog appear normal  but is constantly scratching?  There are signs of pruritus,  hair loss and skin irritation. You take the dog to the veterinarian and he performs a  thorough physical exam to rule out other categories of dermatitis. As your vet continues to ask you questions, he discovers that your dog is outside excavating gopher holes, swimming and romping through fields where thistles are present.  Many dogs are also very sensitive to  lawn grass.  By matching what your vet sees on your dogs skin with a probable environmental irritant, the cause of the skin problem could be determined and corrective actions taken.  Here’s an example. Moist eczema is often called a “Hot Spot.” These skin lesions often occur because of moisture accumulates on the surface of the skin.  Some causes could be that your dog came in contact with pond water, rain or lake water. Small scratches from a thistle could trigger another type of reaction.  If your dog has long or matted hair, it is very possible that moisture on the skin could remain long enough for superficial bacteria to reproduce and cause an infection.  Moist eczema can spread very rapidly and require aggressive therapy to correct. Contact with certain types of plastics could also cause environmental dermatitis. Your vet my prescribe hydrocortisone  medicated lotion or you may be able to pick it up over the counter. In any case, let your vet determine the cause of your dogs dermatitis.