The medical community tends to have a hard time classifying itchiness. It is similar to pain in many respects, though pain makes you want to avoid touching affected areas and itchiness makes you want to scratch. As a primordial impulse, scratching at skin irritations seems to be the nearest source of therapy or release that we have.
The medical term for itchiness is “pruritus.” One of the most common treatments for calming down pruritus is hydrocortisone cream. For mild cases of psoriasis, doctors will sometimes recommend hydrocortisone.
Scratching areas of the skin affected by psoriasis is a bad idea since this tends to compound the problem. It damages the affected area more than the psoriasis would on it’s own, thus opening up the skin to other kinds of infection, thus providing more opportunity for psoriasis flare-ups. For this reason, simply avoiding the urge to scratch is a can be a reasonable first step to treating psoriasis.
Pruritus (itchiness) can be cased by nerve endings in the skin acting up, or it can be initiated from the central nervous system (the brain and the spinal cord). Itchiness can be induced by a variety of stimuli, coming from both inside or from an outside source. For example, if something touches your skin lightly, this can make you want to scratch at that area of your skin.
My take on itching (or why it happens at all) is: The skin itches to let you know that it needs attention or to let you know that something’s not right, much like pain. Thus, allergens and insect bites (poison) give rise to itchiness, so you can know that something is amiss. From a practical perspective, it seems like itchiness might be a mechanism by which the skin sheds dead cells faster than waiting for the wind or gravity to take them away. It makes sense to me that healthy, living skin would want to get rid of old, dead skin.
In the case of psoriasis there is a fine line between itching and stinging pain. On one hand, as stated above, I suspect that the skin itches to inspire the removal of extraneous skin cells (psoriasis makes the body produce so much extra skin that it begins to create scales, or lots of flaky dead skin). Then again, psoriasis has the effect of turning the body against it’s own skin, thus creating a lot of pain and irritation.
