What causes psoriasis skin to look as it does?

Beyond understanding how psoriasis is inherited, researchers have several
theories as to how psoriasis actually develops in people with a geneticpredisposition to it. Recent research suggests several different possible sites
(locations) for the ‘psoriasis’ gene—and there may well be several genes. One
theory is that a lack of control of the outer skin cells leads to the greatly
increased production of cells that characterize psoriasis. This, in turn, may lead
to an abnormality of the blood vessels and the inflammation characteristic of
psoriasis.
Other researchers feel that psoriasis patients have an abnormality in the skin
that leads to inflammation. This inflammation leads to a build-up of white blood
cells from the blood. This build-up of white blood cells then triggers the
thickened skin of psoriasis.
Still another possibility is that the epidermal skin cells fail to mature into the
flat, thickened ‘cornified’ layer they’re supposed to. As a result, the epidermis
tries to produce more cells than usual, leading to the thickened epidermis; this
then leads to inflammation.
A recent theory has suggested that there may be an abnormal immune reaction
in skin with psoriasis. The precise abnormality is not known—it may be a lack of
control of certain cells in the skin that regulate the immune system. This has been
suggested because of the promising results doctors obtained with the immune-
regulating drug cyclosporin. Now researchers have developed new targeted and
safer immune-regulating drugs, e.g. etanercept, infliximab and alefacept, which
block some of these immune changes in the skin. (I will discuss these in more
detail in Chapters 9 and 10.)
Many patients find that symptoms vary over time. There are various reasons
for this. First, infections may prompt or worsen psoriasis. For example, guttate
psoriasis sometimes flares up in patients who are sensitive to bacterial
(streptococcal) sore throats. Some people may get severe psoriasis on the skin-
fold and scalp as a result of a yeast infection in the skin. Stress has also been
named as a major culprit in psoriasis flare-ups. Fortunately, counselling and
relaxation techniques can go a long way towards minimizing the stress trigger
and can be very helpful in keeping psoriasis under control.
Let me stress that most people with psoriasis do NOT have immune
deficiency, nor are they at increased risk of contracting AIDS. If there is an
abnormal immune function in the skin, it is likely to affect only the skin. People
with psoriasis do not display any evidence of general changes in their body’s
immunoregulatory systems.