House Wiki

Dermatitis is a general term to describe any inflammation of the skin.  It is generally characterized by a rash but can also be characterized by bumps, itching  and blisters.

The "horse" cause of dermatitis is a reaction to an irritant, and is often an allergic reaction.  Less common causes are  dry skin, celiac disease, and infection. Ironically, soap and detergent are the most common irritants that lead to dermatitis.  

In many cases, dermatitis can be treated without having to treat an underlying condition.  Anti-inflammatory drugs are often useful and steroid cremes can be useful for some cases, but for some cases can actually exacerbate the condition over the long term.  

Dermatitis at Wikipedia