Is there a simple way of classifying eczema?

Unfortunately, no.
There are many different causes and triggers for eczema – some
from the outside world, for example irritants, allergy and bacterial
infection, and others from within the body. The ones from within
are called ‘intrinsic’ and include ‘atopy’ – having a genetic tendency
to eczema, asthma and hay fever – raised pressure in the leg veins,
and reactions to stressful circumstances. These causes and trigger
factors are not mutually exclusive, so several may be important at
the same time in the same person; it is, however, usually possible
to give a general label to the main underlying cause.
As well as trying to provide an appropriate label, it is often useful
to classify eczema in terms of how long it has been there and how
quickly it appeared. Calling it ‘acute’ suggests a rapid onset and a
short but maybe severe course; ‘chronic’ means continuing for a
long time. This time course may give some extra clues to the trigger
or triggers involved.
Most classifications are imperfect but do serve to show the
different factors involved in producing similar changes in the skin.
Eczema can be classified as follows:
1. Mainly caused by external triggers.
• Irritant – various chemicals, including detergents in soap.
• Physical factors – friction and chronic rubbing, sunlight and
artificial ultraviolet light.
• Allergic – the immune system reacting to something coming
into contact with the skin or taken by mouth.
2. Internal and other causes.
• Atopic – often associated with hay fever, asthma and food
allergies.
• Seborrhoeic – related to yeasts on the skin, which has a
specific pattern.
• Discoid – a descriptive term for rounded patches of eczema
with no obvious cause.
• Venous/varicose/gravitational/stasis – a number of different
terms for eczema on the lower legs owing to problems with
the blood flow and pressure in the superficial veins, which
can be varicose.
• Asteatotic – usually in elderly people and caused by
excessive washing and dry, low-humidity environments.
The skin takes on an appearance like crazy paving.
• Pompholyx – lots of very itchy blisters on the hands and
feet.
• Neuro-dermatitis – often called lichen simplex, this is
linked to chronic rubbing or scratching.