The diagnosis of contact dermatitis depends on a careful medical history, the distribution of the lesions, and patch-testing. Reactions may appear suddenly, or they may present as a chronic, low-grade, smoldering dermatitis. Possible exposures in the home, work, and recreational environment to potential allergens need to be monitored.

Skin patch-testing

The diagnosis is confirmed by patch-testing, a time-honored, well-standardized procedure that is both a test of the skin's immunity and a provocation test that reproduces the disease "in miniature". In the patch test, a suspected contact dermatitis sensitizing agent is applied to normal skin (usually on the upper back) and covered. The patches are removed after 48 hours and the underlying skin examined, with a repeat examination after a further two days. In a positive response, there is inflammation and hardening of skin at the test site. Although there are pitfalls in interpretation, patch-testing is indispensable in the investigation of allergic contact dermatitis.

Diagnosis in TCM places importance on determining the circumstances and manifestations of a disease through inquiry and symptom observation. Diagnosis is based on the traditional four examination techniques:

	Questioning The TCM practitioner will establish the medical history of both the patient and his family.
	Observation Examination of the physical features of the body, such as the face, tongue, hair, nails, sputum (mucus that is coughed up), and location of pain, all offer clues to the problem. The tongue is a particularly useful indicator of the functioning of the internal organs.
	Listening and smelling The smelling of sputum and breath and listening to the sounds produced by the chest offer additional clues to the patient's health.
	Touching Feeling the pulse is a cornerstone of TCM diagnosis and gives the practitioner much information about any bodily imbalance.

Excessive fire mixed with dampness
The lungs have an important role as regulator of the protective qi . The spleen provides nutrients for the skin. If the lungs and spleen are functioning poorly, external pathogens can readily invade the body and fire and dampness evils accumulate. The evils stagnate on the skin meridians causing the appearance of a bullous or blistered rash with edema and leakage of fluid. On examination, the tongue is red and covered with a yellow greasy fur. The pulse is slippery and rapid.

Blood deficiency and wind and dryness accumulation
If the spleen is not functioning properly, there is a decline in acquired jing (essence) and nutrients in the body and this affects the production of blood. This reduction in blood supply causes the skin to lose nutrients. It becomes prone to the development of wind evil and this can turn into dryness evil. The skin appears dry, scaly and thickened. On examination, the tongue is pink and covered with a thin fur. The pulse is taut, thready and rapid.

	In acute eczema, the skin lesion may appear in several forms, there is symmetrical distribution in certain locations and the margins of the rash are usually hard to identify. The condition is of longer duration and can become chronic. There is no obvious contact history with particular substance that could be responsible for the skin condition.
	Facial erysipelas presents with severe systemic symptoms such as chills, high fever, headache and nausea. The rash appears as a red patch of inflamed skin with underlying swelling. The edge of the patch is palpably raised and clearly defined. There is a burning sensation in the lesion and it is tender but not itchy. There is not contact history.