Perhaps the most fallible link in the knowledge of diseases of the skin is their causation. Many dermatoses are cured without our being able to ascertain the cause of the condition for which we have given treatment. Such results are perhaps gratifying from the patient's standpoint but not from our own, as it is highly unsatisfactory to treat a patient for a disease without knowing its cause.
The skin is more exposed to external insults—mechanical, chemical and parasitic—than any other organ. It is perhaps natural that there should exist a considerable diversity of opinion among dermatologists as to the dominance of external versus internal factors in the causation of many diseases of the skin, particularly the inflammatory dermatoses.
The controversy on eczema itself covers a considerable literature. The skin plays a prominent part in immunologic processes in the body, and many so-called eczemas are believed to be of allergic origin.
SCHAMBERG JF, BROWN H. THE CHEMISTRY OF THE BLOOD IN DISEASES OF THE SKINA STUDY OF EIGHT HUNDRED AND SEVENTY-FIVE CASES. Arch Derm Syphilol. 1930;21(1):1–18. doi:10.1001/archderm.1930.01440070009001