The information provided here is not a replacement for a doctor. You shouldn't use it for the purpose of self-diagnosing or self-medicating but rather so you can have a more informed discussion with a professional TCM practitioner.
In Chinese Medicine dermatitis can be treated by one herbs that we have on record. Here is the list below.
Because it is a herb specifically indicated to treat dermatitis as can be seen on Unprepared Rehmannia's page.
Its main actions are: Expels Heat by Cooling Blood. Tonifies Yin by promoting Fluid production. Soothes the Heart by calming Blazing Fire. Cools and nourishes.