Insensible perspiration, also known as transepidermal water loss, is the passive vapour diffusion of water through the

epidermis The epidermis is the outermost of the three layers that comprise the skin, the inner layers being the dermis and Subcutaneous tissue, hypodermis. The epidermal layer provides a barrier to infection from environmental pathogens and regulates the ...

. Insensible perspiration takes place at an almost constant rate and reflects evaporative loss from the

epithelial cell Epithelium or epithelial tissue is a thin, continuous, protective layer of Cell (biology), cells with little extracellular matrix. An example is the epidermis, the outermost layer of the skin. Epithelial (Mesothelium, mesothelial) tissues line ...

s of the

skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other animal coverings, such as the arthropod exoskeleton, have different ...

. Unlike

sweating Perspiration, also known as sweat, is the fluid secreted by sweat glands in the skin of mammals. Two types of sweat glands can be found in humans: eccrine glands and apocrine glands. The eccrine sweat glands are distributed over much of the ...

, the lost fluid is pure without additional

solutes In chemistry, a solution is defined by IUPAC as "A liquid or solid phase containing more than one substance, when for convenience one (or more) substance, which is called the solvent, is treated differently from the other substances, which are ...

. For this reason, it can also be referred to as "insensible water loss". The amount of water lost in this way is deemed to be approximately per day. Some sources broaden the definition of insensible perspiration to include not only the water lost through the skin, but also the water lost through the epithelium of the respiratory tract, which is also approximately per day. Insensible perspiration is the main source of heat loss from the body, with the figure being placed around 480 kCal per day, which is approximately 25% of basal heat production. Insensible perspiration is not under regulatory control.

History

Known in Latin as , the concept was already known to

Galen Aelius Galenus or Claudius Galenus (; September 129 – AD), often Anglicization, anglicized as Galen () or Galen of Pergamon, was a Ancient Rome, Roman and Greeks, Greek physician, surgeon, and Philosophy, philosopher. Considered to be one o ...

in ancient Greece and was studied by the Venetian Santorio Santorio, who experimented on himself and observed that a significant part of the weight of what he ate and drank was not excreted in his faeces or urine but was also not being added to his body weight. He was able to measure the loss through a chair that he designed.

References

Excretion {{anatomy-stub