Regarded as an organ due to its physiological function, it is often stated in articles that "the skin is the largest organ of the human body" when reviewing the literature. But is this fact confirmed by published data?
The skin, the most extensive of our organs?
Why do we say that the skin is the largest organ of the human body?
According to various publications, the skin, while only a few millimeters thick (ranging from 0.5 to 5 mm depending on the area), is considered to be the largest and heaviest of all our organs. Indeed, it can reach up to 1.5 to 2 square meters in total area and weighs approximately 4 kg, thus representing between 5 to 10% of the total body mass of an average adult, depending on height and body type.
Is this claim validated?
In terms of weight, the skin can be considered the largest organ compared to average-sized organs, such as the brain (typically between 1.3 and 1.5 kg), the heart (averaging 250 to 350 g), or the liver (averaging 1.5 kg). However, the weight of the skin is not comparable to the large organs of the musculoskeletal system, including muscles, ligaments, skeleton, cartilage, and connective tissues. It gives your body its shape, support, stability, and countless other important movements for your body. Studies have determined that human skin, including the epidermis and dermis, weighs 3.86 kg, which represents 5.5% of the total body weight of an average human weighing about 70 kg.
Indeed, it has been reported that the skeleton accounts for 14% of the human body weight (approximately 22 lbs) and 42% if we are talking about skeletal muscles. Furthermore, it has been reported that an average adult male is composed of 42% skeletal muscles, while an average adult female is composed of 36%. If we were to include subcutaneous fat, the skin would be, in terms of mass, the largest organ of the human body. However, for some, subcutaneous fat is not officially considered part of the skin.
The skin cannot be considered the largest human organ in terms of exchange surface area. The body surface of an average man weighing about 70 kg is approximately 1.8 m2. In comparison, the exchange surface of the respiratory pathways in the lungs has been estimated at 70 m2, roughly half the size of a tennis court. The surface of the mucous membrane of the human gastrointestinal tract has been estimated to be the size of a football field (300 to 400 m2). Therefore, human skin cannot be considered the largest organ of the human body, neither in terms of weight nor in terms of exchange surface area.
What would then be the largest organ of the human body?
A recently published study has highlighted the discovery of macroscopically visible spaces within tissues that had never been evaluated before, filled with interstitial fluid, which are dynamically compressible and distensible, and supported by a complex network of thick collagen bundles. This structure was detected in the dermis, the gastrointestinal tract, the lungs, the urinary bladder, between muscles, around blood vessels, and more. This tissue is believed to have a uniform anatomical structure and function throughout the body. Widespread, this new anatomical pattern could be the most extensive organ in the human body, occupying a volume greater than that of the skin. However, further investigations are needed to confirm this claim.
GOLDSMITH L. A. My organ is bigger than your organ. Archives of Dermatological Research (1990).
SONTHEIMER R. D. Skin is not the largest organ. Journal of Investigative Dermatology (2014).
THEISE N. D. & al. Structure and distribution of an unrecognized interstitium in human tissues. Scientific Reports (2018).