Surprisingly, early physicians and scientists had little interest or regard for human skin. Greek philosopher and scientist Aristotle believed that skin was an afterthought, passively produced like a rind on cheese. Roman anatomist Galen considered the skin to be just an annoying wrapper, hiding the more significant mysteries hidden beneath.

Late in the 18th century, Austrian physician and amateur botanist Dr. Joseph Von Plenk began to document and name the dermatologic ailments he frequently encountered by applying the word “lichen,” relating directly to his interest in plants. Names such as ‘’lichen planus” (flat lichen), “lichen aureus” (golden lichen), and “lichen simplex chronicus” (simple, chronic lichen) still bear the names he gave them. Then in the early 19th century, two skin afflictions were named for their resemblance to a wolf’s bite: “lupus vulgaris” and “lupus erythematosus.”

The first physician to formally recognize the essential functions of the skin was Sir Thomas Chevalier, who was the “Surgeon Extraordinaire” to the king of England in 1823. Among other things, he observed that neonatal skin developed late in the gestational cycle, suggesting that this was one of the final developmental activities before the emergence of the child.

This was a prescient observation, since we now know that immaturity of the skin and its critical barrier functions is the paramount obstacle to the survival of an extremely premature infant. But astoundingly, another 130 years would pass before the true nature and importance of the skin’s permeability barrier began to be fully understood.

“In my paper of 1964, which established that the horny layer was a tissue made up of corneocytes… I did not go any further than asserting that the stratum was a cellular barrier, the end product of a viable epidermis whose raison d’etre was to produce the dead stratum corneum. I did not have the vision to foresee that the stratum corneum would become very much alive.”

Albert M Kligman, M.D.

New discoveries

Before the 1960’s, the stratum corneum was usually described as the simple, biologically inactive outer layer of the epidermis, a lattice structure of dead keratin and epidermal cells in the final stages of desquamation – the sloughing off of the outer layer of the skin. However, scientists did not realize then that the process of hematoxylin and eosin (H+E) staining, used to prepare slides for examination under a light microscope, was dramatically altering its appearance, resulting in a misleading and inaccurate depiction of the actual structure of this vital tissue.

“Perhaps no tissue is so physically maligned by processing for… microscopy as is the stratum corneum… No tissue of such critical importance for survival has been so intellectually maligned.”

Peter M. Elias, MD

In the 1960s and early 1970s, researchers at Harvard University and elsewhere were finally able to separate the stratum corneum from the rest of the skin and examine frozen sections stained with hydrophobic dyes. This is when researchers began to discover the true nature and function of this very thin tissue.

During this period, a critical body of evidence grew about stratum corneum structure, biochemical composition, and critical and essential functions. By the mid-1970s, irrefutable evidence had emerged about the true structure and biology of the stratum corneum, although it took some time to achieve widespread acceptance of this early work.

Today, our understanding of the formation, structure, composition and maturation of the stratum corneum continues to grow steadily. There is now a broad consensus among researchers that this outermost layer provides a truly magnificent barrier to water loss, allowing humans to exist in a “dry” terrestrial environment. Current research is exploring how the skin’s complex mechanisms respond to environmental challenges and skin surface trauma.

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