Dermatitis usually appears as a rash, and may cause itching, blisters, swelling, and often scabbing and scaling. It often marks an allergic reaction of some kind. Contact dermatitis is caused by something (often a chemical) touching the skin. Atopic dermatitis usually affects the insides of the elbows, the backs of the knees, and the face; generally resulting from an inherited sensitivity, it's often triggered by inhaling something. Eczema, psoriasis, and dandruff are all forms of dermatitis. Even in the worst cases, dermatitis isn't infectious and doesn't produce serious health consequences.