Allergies, viral infections, parasites or any systemic disease can lead to dermatitis. Secondary infections may infiltrate untreated lesions.
Redness, swelling, cracking are the leading symptoms. There can also be crusting or scabbing of the area.
Treatment begins with a careful evaluation of the recent history of the animal. Local treatment will only be a temporary solution until the underlying cause has been found and treated. Clip the hair from the area. If the inflamed area is moist, you would want to use medications that are drying in nature (astringents such as rubbing alcohol, iodine); if the area is dry and cracking, moist preparations (ointments such as udder balm, aloe vera, steroid ointments) should be applied. If the patient tends to make matters worse by chewing on the sores, systemic steroids can be obtained from your vet to help reduce the irritation.
Keep your animals clean and free of parasites. Be aware of things that they might be allergic to.
There is a "fun" type of dermatitis: idiopathic dermatitis. This is when you go to the vet and he/she says, "Oh, no problem, this is idiopathic dermatitis." And you carry home a lot of expensive remedies which may or may not take care of Suzie Q’s problem. If you look up the term, you will find it means any inflammation of the skin that we don’t know the cause of.