Dermatitis is inflammation of the skin (i.e. rash). This is a vague term used to lump together anything that causes the skin to be inflamed. This can be due to contact allergies (contact dermatitis) from coming into contact with a topical allergen like poison ivy, or can be from rheumatic condition where the body attacks itself.  Knowing the type of dermatitis may help you find a more successful treatment. However, if you do not know this may be a good starting point.