Dermatitis is a blanket term meaning "inflammation of the skin" (i.e. rash).
There are several different types of dermatitis. The
different kinds usually have in common an allergic reaction to specific
allergens. The term may be used to refer to eczema, which is also known
as dermatitis eczema or eczematous dermatitis.

Dermatitis primarily on the non-dominant hand develops in workers who grip an object while performing a more delicate task, often with a tool, with the dominant hand. This right-handed optician recalled only after patch-testing positive to ethyl acrylate that he sometimes held heated acrylic frames in his left hand, which caused his dermatitis. Image Credit: CDC
A diagnosis of eczema
often implies atopic dermatitis (childhood eczema), but without proper
context, it means nothing more than a "rash".

Clothing dermatitis is commonly the result of permanent press finishes used in the manufacture of uniforms and other clothing items. Detergents and fabric softeners result in a similar pattern of dermatitis. The axillary vault is typically spared, with dermatitis involving the rim of the axilla. Image Credit: CDC
In some languages, "dermatitis" and eczema are synonyms,
while in other languages "dermatitis" implies an acute condition and
"eczema" a chronic one. The two conditions are often classified
together.
Further Reading
This article is licensed under the Creative Commons Attribution-ShareAlike License.
It uses material from the Wikipedia article on
"Dermatitis"
All material adapted used from Wikipedia is available under the terms of the
Creative Commons Attribution-ShareAlike License.
Wikipedia® itself is a registered trademark of the Wikimedia Foundation, Inc.