Skin is made up of three main layers €“ the epidermis, the dermis and subcutaneous tissue. The epidermis is mostly comprised of keratinocytes, which are formed in the lowest layer and mature as they move towards the surface, where they are gradually worn away and replaced.

The dermis is thicker and contains many different structures, including blood vessels, nerves and proteins, such as collagen. Sweat glands and the base of hair follicles are also in the dermis. The innermost layer, the subcutaneous tissue, is an important insulator as it regulates the body's temperature. It also helps to protect the vital internal organs.

Human skin has many roles €“ from helping to regulate body temperature to assisting in vitamin D production, as well as acting as a barrier against harmful agents, such as bacteria and chemicals.

While healthy skin is an effective barrier that keeps moisture in, and bacteria and irritants out, dry skin is noticeably less effective. Picture the skin as a brick wall: the bricks are cells being held together by mortar €“ fats and oils. An eczema patient may not produce enough fats or oils, which means their skin is less capable of retaining water.

When skin cells lack water, they shrink, which causes gaps to open up between them. If bacteria and irritants get through the cracks into the deeper layers, the skin becomes irritated and inflamed. This can lead to redness, itching, cracking, fissures and secondary bacterial infections.