The Organ of the Body

Skin is active, living tissue that acts as tough armor to keep harmful microbes and strong rays of light away from more sensitive internal organs. It also relays sensory information like pain, texture and temperature to the rest of the body.


The top layer, the epidermis, contains cells (keratinocytes) that are continually shed or pushed to the surface. It also contains melanocytes that give skin color and sweat glands.

Protective Barrier

The skin is an amazing organ that performs a multitude of vital functions. The outermost layer, known as the stratum corneum, is often described as a brick wall that literally keeps harmful environmental stressors out of the body. It consists of tough skin cells called corneocytes, bound together with mortar-like lipids. This barrier serves to keep various harmful environmental toxins and infectious pathogens from penetrating the body at a molecular level. In addition, it also prevents the water inside the body from escaping and evaporating at the surface of the skin.

This barrier is maintained by a thin layer of lipids and fatty acids, which helps to regulate the pH balance of the skin as well as protect it from microorganisms like bacteria, fungi, and viruses. It is also assisted by the presence of antimicrobial peptides and antimicrobial lipids.

In order to preserve the integrity of this barrier, it is important to use a properly-formulated skincare routine that includes proper cleansing and moisturizing. A good way to do this is with products that contain the OS-01 peptide, which has been clinically shown to significantly increase the thickness of the epidermis of lab-grown ex vivo human skin models. It is also recommended to use a moisturizer that contains humectants, which help prevent water loss from the surface of the skin. These can include glycerin, honey, urea, and hyaluronic acid.

Sensory Perception

In addition to allowing your body to sense touch, the skin also has sensory receptors that detect pain, temperature and pressure. These sensory receptors send signals to the spinal cord, which in turn sends information to a part of your brain called the somatosensory cortex in the parietal lobe. This specific flow of information is what enables you to perceive the world around you, including the physical properties of your hand cream.

Sensory judgments of bulk rheological properties, such as viscosity, are quite common in tactile perception studies. However, many of these studies use instrumental measurements that do not necessarily correlate well with perceptual quantities. One problem is that the results of these instrumental studies may not generalize to product-treated human skin (in vivo).

The sensitivity of individual skin locations to the pressure differences that can be perceived via the mechanoreceptor innervation density is another issue. Despite these limitations, recent experimental work is providing promising signs that mechanical events at the surface of the skin can be related to perceptual quantities in a meaningful way.

For example, some studies have found that people can distinguish a soft versus a stiff hand cream by the amplitude of vibrations generated at the skin’s surface. Other studies have shown that changes in the mechanical properties of skin, such as loss of compliance, correlate with ratings of product performance.

Immunologic Surveillance

The immune system provides vertebrates with an effective means to recognize and respond to microbial pathogens, as well as to protect against physical insults such as burns. Its complexity, involving a wide range of cell types that express antigen-specific T and B cells, offers an unparalleled flexibility in responding to different microbes and environmental insults. The ability of vertebrates to develop adaptive immune responses also allows them to maintain memory of prior exposures and response to them in a more targeted manner.

The key to immune surveillance is the interaction between antigen-presenting cells (APCs) and naive T cells. In the skin, activated dendritic cells derived from epidermal Langerhans cells or dermal DCs are professional APCs that bind foreign antigens and present them to naive T cells circulating in the specialized microenvironment of the draining lymph nodes. This increases the likelihood that a naive T cell will encounter and be stimulated by its cognate antigen, thereby eliciting an effector response.

Regulatory T cells also participate in immune surveillance at the skin interface. In humans with the autoimmune disease psoriasis, the imbalance between effector and regulatory T cells is reflected in the development of erythematous cutaneous plaques covered with scales. In addition to regulating inflammatory responses, these regulatory cells have been shown to inhibit progression of solid tumours derived from chemical carcinogens in the DMBA/TPA model of squamous cell carcinoma.


The skin regulates our internal body temperature to keep it within a healthy tolerance range, even when the external environment is changing. It does this by adjusting blood flow through the skin to maintain core temperature. Vasodilation allows heat to escape into the ambient air via radiation, convection and evaporation, while vasoconstriction helps retain the body’s heat. It also regulates our sweating by limiting the amount that can be lost from the surface of the skin.

Thermoregulation is one of the body’s first-line autonomic defences against heat and cold. However, the thermoregulatory responses that are recruited to protect against thermal insults require a substantial resource commitment (energy and water) and cannot be triggered until deep body temperatures start to change. This may explain why peripheral temperatures are generally more important for triggering most (but not all) thermoregulatory behaviours, while the thermoregulation of the deep body is mainly triggered by its own metabolic processes.

It is a widespread assumption that cutaneous nerves detect environmental thermal signals and that they serve as feedforward inputs to the thermoregulation system. Nevertheless, several recent papers (Romanovsky et al 2009, Werner 2010 and Nakamura 2011) have questioned this assumption by suggesting that skin temperature represents not the body’s own but the ambient temperature, which would render cutaneous thermal signals irrelevant as feedback to the thermoregulation system.