While driving to work one morning, I heard a radio commercial for a men’s fragrance product. In that commercial, the male actor boldly stated that “the skin is the largest organ.” Additionally, I had heard or read this same statement several times earlier that same week.

Dictionaries define dictum (synonyms: saying, proverb, maxim, aphorism) as a formal pronouncement from an authoritative source or a short, pithy expression identified with a particular person. Because of its “pithiness,” dictums are often taken as fact. However, in the case of the dictum “the skin is the largest organ,” this is not the case.

In 2014, I published a letter to the editor of the Journal of Investigative Dermatology titled “Skin is not the largest organ.” In that letter, I reviewed the published literature that both supported and denied the idea that the skin is the largest human organ.

Lowell A. Goldsmith, MD, was a pioneering investigator and thought leader in the modern era of human skin biology, biochemistry, and genetics. Dr. Goldsmith had an early interest in the weight of the skin compared to other organs in the human body. His calculations determined that the human skin (epidermis plus dermis) weighs 3.86 kilograms or 5.5 percent of the total body weight of the proverbial 70 kg man. Others reported that human skin accounts for about 15 percent of body weight. However, those reports did not clearly state that the fatty “subcutaneous” tissue located below the skin was excluded from their calculations.

Wikipedia also states that human skin is the largest organ. However, that repository of electronic conventional wisdom also states that the skin is composed of the epidermis and dermis. It specifies that the hypodermis (subcutaneous tissue) underlies the skin but is not part of the skin. Some modern authorities feel that human subcutaneous tissue itself should be considered a separate endocrine organ.

The human skeleton accounts for about 15 percent of the human body’s weight. In addition, it has been reported that 30 to 40 percent of an average adult’s weight is made up of muscle tissue. Therefore, based on weight, the musculoskeletal system, which comprises approximately half of the body’s weight, is by far the largest organ system in the human body.

Nor can the skin be considered the largest organ based on functional surface area. The body surface area of the proverbial 70 kg man is 1.7 square meters. By comparison, the gas-exchanging surface of the lung’s airways has been estimated to be 70 square meters. This is a bit under one-half the size of a singles tennis court. The absorptive mucosal surface area of the human gastrointestinal tract has been estimated to be the size of an American football field.

When common knowledge is found to be false, what are we to do? We now live in a world where, theoretically, every human being in the world’s population of 8 billion could instantly share their thoughts, emotions, misconceptions, biases, and falsehoods with every other person in the world. While freedom of expression is a foundational element of democracy, there have to be limits. For example, yelling “fire” in a crowded theater that is not on fire cannot be tolerated.

The peer-reviewed scientific process is one of the few institutions in modern society that has baked into it a process for minimizing or eliminating bias. Perhaps that process could serve as a model for addressing bias in official electronic civil discourse. However, that could be challenging, as artificial intelligence in its current form also contains bias—the bias of the software engineers who created its code.

Do not fall for the “dermatologist-approved” gimmick when considering the purchase of an over-the-counter skincare product or a skin treatment. That phrase means absolutely nothing about the product’s efficacy or safety.

At the time that my letter to the editor was published in the Journal of Investigative Dermatology, Dr. Lowell Goldsmith was its Chief Editor. During the peer review process, he and I had a delightful debate concerning the merits of my letter for publication in this prestigious medical research journal. Dr. Goldsmith was one of the “giants who walked the wards” during my medical training years. Lowell passed away on July 10, 2024. I would like to dedicate this piece to his memory.

Richard D. Sontheimer is a dermatologist.