Paul Gerson Unna: The Dermatologist Who Put Skin Under Glass
He was the leading dermatologist in Europe for thirty years before any university would give him a chair. Paul Gerson Unna ran his laboratory in Hamburg as a private citizen, financed by his own practice, and physicians from every continent came to it anyway. He was sixty-eight when the University of Hamburg finally appointed him its first professor of dermatology in 1919 — an honour that confirmed what the profession had already conceded decades earlier: that the science of skin had been rebuilt, largely by one man, entirely outside the academy.
Hamburg, Heidelberg, and a War
Unna was born in Hamburg on 8 September 1850 to Moritz Adolph Unna, a physician, and Ida Gerson. He began medicine at Heidelberg and had to break off to fight in the Franco-Prussian War, where he was severely wounded — a fact worth pausing on, since the man who would spend his life on the fine structure of skin nearly lost his own to a bullet at twenty.
He resumed in 1871, studying at Heidelberg and Leipzig, and took his doctorate under the great anatomist Heinrich Wilhelm Waldeyer at Strasbourg. His 1876 dissertation was on the histology and development of the epidermis, and it set the direction of everything that followed: from the beginning, Unna's question was not what a rash looks like but what the tissue is doing. For clinical training he went to Vienna, to the school Ferdinand von Hebra had built, working under Hebra, Moritz Kaposi and Heinrich Auspitz.
The Dermatologikum
In 1881 he opened a practice for skin disease in Hamburg, and in 1884 expanded it into a hospital at Eimsbüttel. What he actually created was something no university then offered: a single institution combining a clinic, an outpatient department, research laboratories and a museum. It became a world-respected teaching institution, and its pupils — Americans, Britons, Russians, Japanese — carried his methods home. For a generation, to be seriously trained in skin pathology meant a period in Hamburg.
His position was unusual and deliberate. Unna was an independent practitioner who funded fundamental research out of clinical income, answerable to no faculty and no ministry. It gave him freedom and cost him institutional recognition until very late.
Inventing Dermatopathology
Unna's central achievement was to make the microscope the primary instrument of dermatological diagnosis. Hebra had classified skin disease by pathological anatomy as it could be seen with the naked eye and the scalpel; Unna took the classification down to the cellular level, and in doing so effectively created dermatopathology as a discipline.
Doing so required inventing the means. Tissue must be stained before its structures become visible, and the stains available in the 1880s were not adequate for skin. Unna became one of the era's most inventive histochemists, devising staining methods to make specific cell types and structures declare themselves — among them the pararosanilin-iodine technique developed in his work on the bacteriology of leprosy. The payoff was descriptive: he first defined the stratum granulosum, the granular layer of the epidermis, and he described the plasma cell, a discovery whose significance for immunology far outran dermatology.
He set out the whole programme in *Die Histopathologie der Hautkrankheiten*, which established him as the world authority on the subject and remained a standard reference for decades. He coined the term *acanthosis nigricans* in 1889, first defined seborrhoeic eczema in 1887 — now called Unna's disease — and in 1892 identified the causative organism of soft chancre. In 1894 he introduced projection of slide images for the teaching and examination of skin, so that a room could look at the same specimen at once. He co-founded the *Monatshefte für praktische Dermatologie* in 1882, which became a principal German-language journal of the field.
From Microscope to Marketplace
Unna's other track was therapeutic, and it is the reason his name reaches people who have never heard of dermatopathology. He described the keratolytic action of salicylic acid in 1882, and introduced ichthyol and resorcinol into the treatment of skin disease in the mid-1880s — agents still on pharmacy shelves.
More consequentially, he worked with the Hamburg pharmacist Carl Paul Beiersdorf on the manufacture of medicated plasters and gauzes, a collaboration that turned a set of clinical ideas into an industry. Out of it came the Leukoplast adhesive bandage in 1899 and the Unna boot, a compression dressing of zinc-oxide-impregnated gauze applied to the lower leg for venous ulcers. Well over a century later, the Unna boot is still applied in wound clinics, essentially unchanged.
Recognition, Eventually
The institutions came round slowly. The Hamburg senate granted him the title of professor in 1907; he became chief physician at Eppendorf Hospital in 1908; and the university chair arrived in 1919. He died in Hamburg on 29 January 1929, in the city where he had been born seventy-eight years earlier and had spent almost his entire working life.
Why Paul Is Called a Genius
The distinctive quality here is method-invention — the recognition that a field's questions cannot be answered until someone builds the tools, followed by the willingness to go and build them. Unna wanted to know what was happening in diseased skin at cellular resolution, found that existing stains would not show him, and so became a chemist to make stains that would. The plasma cell and the stratum granulosum were not lucky sightings; they were the predictable yield of an apparatus he had constructed to make such things visible. He then did the same thing on the treatment side, reasoning from the physical properties of skin to the design of a dressing, and taking the trouble to see it manufactured properly. Very few scientists operate competently at both the histochemical bench and the factory floor.
The honest counter-case: Unna was not a theorist, and he left no general principle behind him. His contributions are a long series of techniques, descriptions, stains and preparations rather than an idea that reorganised biology; the plasma cell mattered enormously, but its significance was established by immunologists who came later. He worked outside the university system and, some argued, outside its scrutiny — his commercial partnership with Beiersdorf, admirable in its results, sat uncomfortably close to his clinical authority in a way a modern reviewer would flag. The Indian dermatological journal that published a centenary tribute headlined him a "genius of all times," which is the language of homage rather than assessment. A cooler judgement is that Unna was a craftsman-scientist of the highest order: not a man who changed how we think, but one who changed what could be seen, which in a visual and structural discipline amounts to nearly the same thing.
Legacy
Unna's name survives in a scatter of places that do not obviously belong together — Unna's disease, Unna–Thost syndrome, the Unna boot, Unna's paste — and in the Beiersdorf company, which outgrew its founder's plasters. What holds them together is a single habit of mind. Unna treated the skin as an object of physical investigation with its own chemistry, its own architecture and its own engineering requirements, and he refused to accept that a question was unanswerable simply because no existing instrument could answer it. Every dermatopathology report written today is a document in the format he invented.
Achievements
- Held posts at University of Hamburg
- Fields: dermatology
