What happens in the skin of people with eczema?

To explain what happens in eczema, you need to understand the
structure of the skin as seen down a microscope. The skin consists
of three layers:
• The outer layer is called the epidermis. This contains a
‘brick wall’ of skin cells (keratinocytes) that are held
together by a cement (the mortar) mostly made up of fats
or lipids. The many different layers start with live cells that
constantly reproduce, creating new cells that move up to
the surface, die and are shed. This whole process takes
about 28 days. The lipid cement makes the brick wall into a
very effective barrier against the environment. It prevents
the skin losing too much water and prevents noxious
(poisonous) substances getting in.
• The middle layer is called the dermis. This consists of
tough structural fibres called collagen and elastin, which
provide strength and elasticity to the skin. It also contains
blood vessels that supply nutrients and oxygen to both the
dermis and the epidermis.
• The deepest layer of the skin is called the subcutis and is
predominantly made up of an insulating layer of fat.
In eczema, it is the dermis and epidermis that are affected. The
epidermis shows the most marked changes. The inflammation leads
to leaky blood vessels, so fluid collects between the keratinocytes,
causing them to separate. The brick wall takes on a sponge-like
appearance. As the eczema becomes chronic, the constant rubbing
and scratching causes the epidermis to regenerate more quickly,
so it becomes thickened.
Finally, eczema causes changes in the upper part of the dermis.
This region becomes flooded with white blood cells, which are part
of the body’s immune system or defences. They leak out of vessels
and even pass up into the epidermis. Current evidence suggeststhat it is these cells that drive the whole process of inflammation
in the skin.