Learn About the Skin

Why is your skin important?

Skin is the largest body organ, and a major site for allergic disease, such as eczema. As an interface with the environment, skin protects the body from the pathogens, environmental toxins and other dangers. Skin also provides a physical barrier – without skin, all the water would evaporate from the body, and any bacteria, virus or chemical could get directly to all the important organs inside your body. Skin plays also an important sensory function, as the nerve endings inside the skin help to feel heat, cold and pain.

A Career in Skin Research

Professor Peter Friedmann is an expert in skin immunology and has dedicated his career to researching immune functions and disease in the skin. Below is a talk that Prof. Friedmann kindly gave at our Defend the Skin grand final, in which he gives a fascinating insight into his career and research, as well as explaining more about the role that skin plays as part of the immune system.

Structure of the skin

The skin is made up of a number of layers. Starting from the bottom, we have the subcutaneous fat layer, followed by the dermis. Next, we move into the epidermis, which itself is seperated into several layers. At the bottom of the epidermis, we can see a very thin layer of keratinocytes, known as basal keratinocytes. These cells continually divide and replenish the epidermis with new cells. Above them we find the spinous layer, followed by the granular layer, and finally, the cornified layer. Keratinocytes act as the building blocks for all of the layers in the epidermis, but as the basal layer generates new cells, the keratinocytes in the higher layers start to die, or become cornified. By the time they reach the cornified layer, the keratinocytes have become corneocytes and are ready to be shed by the body.

Cells in the skin


Form the outermost layer of the epidermis, protecting from the outside environment

Basal Keratinocytes

Younger keratinocytes underneath replace dead ones in a few days.

Langerhans Cells

Langerhans cells sense outside dangers to the skin and tell the immune system when to act

Dermal Dendritic Cells

Direct the immune responses in the dermis


“Large eaters” – engulf and destroy pathogens and tissue debris

Mast Cells

Store bioactive substances in granules, which can be released immediately when they sense danger

T Cells

Cells of adaptive immune system, can tailor the immune response to a specific pathogen – and create a long lasting memory cells ready to respond efficiently to the same danger

Immune responses in healthy skin

In order to be able to provide immune protection, skin is populated by multiple subsets of immune cells, including Langerhans cells, dendritic cells, macrophages and T lymphocytes. Dendritic cells (DCs) are special cells in the immune system that can recognise ‘safe’ pathogens from ‘dangerous’ ones. When a DC comes into contact with a harmful bacteria or virus, it can sense that it is dangerous. Alarm bells are activated and DCs recruit other immune cells to kill the invaders. Unfortunately in allergy, DCs misidentify ‘safe’ components of our own bodies or harmless substances as ‘dangerous’. This therefore leads to uncontrolled activation of the immune system that attacks areas of our own body. Currently little is known about how DCs in healthy people stop our immune system activating against ‘safe’ pathogens. Our aim is to identify molecular “switches” regulating this ability. Increased understanding of this process could lead to drug development that re-installs the ability of DCs to distinguish ‘friend’ from ‘foe’, therefore preventing allergy.

What happens when things go wrong?

All the cells of the skin need to function correctly, otherwise the skin (and other parts of your body) can become ill. For example, if keratinocytes do not stick together well enough, the skin barrier is compromised, and bacteria and other substances can go through, causing inflammation. If the cells of immune system get too activated, they can produce bioactive substances, making your skin itch, swell, and cause a lot of discomfort.

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