Misconception: The skin is the largest organ of the body.

Why is it said that the skin is the largest organ of the human body?

According to various publications, the skin, although only a few millimetres 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 m2 in surface area in total and weighs approximately 4 kg, thus representing between 5 to 10% of the total body mass of an average adult, depending on height and build.

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 around 70 kg.

Indeed, it has been reported that the skeleton accounts for 14% of the human body weight (approximately 10 kg) and 42% if we are referring to skeletal muscles. Furthermore, it has been reported that an average weight adult male is composed of 42% skeletal muscles, while an average weight adult female is composed of 36%. If we were to include subcutaneous fat, the skin would, in terms of mass, be 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 as 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 of 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 as 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 has been 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.