Dermatitis is when the skin gets irritated and inflamed, and Chronic Dermatitis is when this irritation is a recurring or prolonged problem.
A common cause of chronic skin irritation is Eczema, or Atopic Dermatitis, which is a patch or patches of skin that are consistently inflamed due to genetics or environmental changes. Another cause is contact with an allergen on a regular basis, creating irritation every time you are exposed.
Chronic Dermatitis caused by Eczema typically occurs in those who have a genetic history of the problem, and it occurs most often in young children. Although Eczema is mostly experienced by kids, Chronic Dermatitis can affect a person at any age. Individuals who suffer from allergies are more likely to develop rashes than those who do not, as do those who work in a high allergen environment.
Depending upon the severity of case, Chronic Dermatitis may be able to be treated using an improved skin care routine that utilizes medicated lotions. More severe forms of the recurring skin rash may require oral medications prescribed by a medical professional. If the Chronic Dermatitis is caused by an allergen, it is necessary to try to remove that allergen from your daily life in order to stop the skin problems from reoccurring.
http://www.mayoclinic.org/diseases-conditions/dermatitis-eczema/basics/definition/con-20032183