Psoriasis - Causes

Stress and Strong Emotions. Stress, unexpressed anger, and emotional disorders, including depression and anxiety, are strongly associated with psoriasis flare-ups. In one study, nearly 40% of patients remembered a specific stressful event that occurred within a month of a psoriasis flare. A 2001 study suggested that stress can trigger specific immune factors associated with psoriasis flares. Some evidence indicated that people with psoriasis may respond to stress differently from those without the skin disease. In one study, psoriasis patients had fewer aggressive verbal responses than others did when confronted with hostile situations.

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Infection. Infections caused by viruses or bacteria can trigger some cases of psoriasis. Some examples include the following:

Streptococcal infections in the upper respiratory tract, such as tonsillitis, sinusitis, and so-called "strep" throat, are known to trigger guttate psoriasis in children and young adults. The infections may also worsen ordinary plaque psoriasis.
The human immunodeficiency virus (HIV) is also associated with psoriasis.
An uncommon form of human papillomaviruses (HPV) called EV-HPV has been associated with psoriasis. Although EV-HPV is probably not a direct cause, it may play an indirect role in the perpetuation of psoriasis. (This HPV form is not the virus associated with cervical cancer and genital warts.)
Helicobacter pylori (H. pylori) infection, a major cause of peptic ulcers, has been proposed as a possible cause of psoriasis. Research in 2001 indicated that this is highly unlikely, at least in children.

It seems reasonable to assume that pustular psoriasis, which resembles an infection, is caused by some organism, but none to date have been identified.

Skin Injuries and the Kbner Response. The Kbner response is a delayed response to skin injuries, in which psoriasis develops later on at the site. In some cases, even mild abrasions can cause an eruption, which may be a factor in the frequency of psoriasis on the elbows or knees. (It should be noted that psoriasis can develop in areas with no history of skin disruption.)

Drugs. A number of drugs can worsen or induce pre-existing latent psoriasis, including the following:

The anti-malarial drug chloroquine.
Certain drugs used for hypertension and heart problems, including angiotensin-converting enzyme (ACE) inhibitors. Beta-blockers may actually trigger the onset of psoriasis and produce flare-ups in people who already have it.
Progesterone used in female hormone therapies.
Lithium, which is used in bipolar disorder. (It may trigger the onset of the disease and cause severe flare-ups in people who already have psoriasis.)
Indomethacin, a non-steroidal anti-inflammatory drug (NSAID), can cause or worsen psoriasis. (Other NSAIDs, such as meclofenamate, may actually improve the condition.)
Withdrawing from oral steroids or high-potency steroid ointments that cover wide skin areas can cause flare-ups of severe psoriasis, including guttate, pustular, and erythrodermic psoriasis. Because these drugs are also used to treat psoriasis, this rebound effect is of particular concern.
Agents that cause rashes, a side effect of many drugs, can trigger psoriasis as part of the Kbner response.