HX33 From microscope to marketplace: the 175th anniversary of Paul Gerson Unna’s legacy

Abstract Paul Gerson Unna (1850–1929) was a pioneering figure whose contributions spanned the entire field of dermatology. Widely recognized as the founder of modern dermatopathology, he played a crucial role in bridging the clinical, histological and therapeutic facets of dermatology. Born into a family of physicians in Hamburg, Unna studied at the University of Heidelberg under renowned dermatologists, including Heinrich Wilhelm Waldeyer, Ferdinand von Hebra, Moritz Kaposi and Heinrich Auspitz. In 1881, he established the Dermatologikum, a private dermatology clinic in Hamburg, which became a prominent centre for dermatological research and education. In 1882, he founded Monatshefte für praktische Dermatologie, a journal that promoted international collaboration. His reputation as a brilliant educator attracted postgraduate scholars worldwide to attend his dermatology courses. In 1907, Hamburg’s senate recognized his contributions by awarding him the title of professor. A major part of Unna’s legacy lies in his innovative contributions to dermatopathology. He had groundbreaking ideas regarding tissue stains that led him to develop over 100 staining techniques. These allowed him to identify collagen and elastic fibres, plasma cells and intracellular proteins, and to describe processes such as acanthosis and spongiosis. He was also the first to describe the stratum corneum and its three distinct layers. One of Unna’s most significant works was his Histopathology of Skin Diseases (1894), a 1200-page text that classified skin diseases based on their histological features discovered at the time, rather than their clinical morphology. This pioneering approach provided a novel, albeit controversial, outlook on pathologies, including his classification of naevi. Additionally, Unna was one of four authors of the International Atlas of Rare Skin Diseases, and he was the first to describe seborrhoeic dermatitis. It was initially known as morbus Unna and his name remains attached to a number of other conditions, such as Unna–Thost palmoplantar keratoderma. Unna’s work extended to include experiments with dermatological treatments. He collaborated with pharmacologists to develop medicated soaps containing active ingredients like salicylic acid. He also invented the Unna boot, a specialized compression bandage steeped in zinc oxide, and modified versions are still in use today to treat venous ulcers. Unna’s discovery of Eucerit, an emulsifier, and further collaboration with Paul Beiersdorf paved the way for NIVEA Creme, one of the earliest modern cosmetic creams. With over 500 published works on skin pathology, microbiology, biochemistry and pharmacology, Unna made contributions that shaped modern dermatology. His legacy lives on through his lasting influence on both medical dermatology and the skincare industry.