To people who have never had it, psoriasis is “just a skin disease.” But psoriasis is more than skin deep; it is an inflammatory disease. The exact cause is not known, but it is not caused by infections of the skin. Research findings suggest that psoriasis may be caused by a problem with the body’s immune system. On the basis of these research findings, psoriasis is increasingly being referred to as an “immune-mediated” or autoimmune disease. An autoimmune disease is any condition caused by the immune system attacking the body’s own tissue.
Most skin cells divide and replace themselves about once a month (every 28 to 30 days). As new cells emerge, the old skin cells on the surface die and are shed. For most people, the process is so subtle that it’s barely noticeable.
In someone with psoriasis, this process is not working properly. Instead of reproducing every month, the skin cells in the affected areas reproduce every 3 to 6 days. As a result, the number of skin cells increases enormously. With so many new cells emerging so quickly, they accumulate on and just under the skin, causing a raised, scaly lesion or patch. In its most common form (plaque psoriasis), the scales on the surface of the skin flake off easily, causing a white or silver scale. The cells below the surface stick together and form lesions that are tender, red and likely to bleed.
A “psoriasis gene” has not been identified, but psoriasis may share parts of genes linked to other autoimmune and inflammatory diseases. This may explain why people with psoriasis may also have other diseases such as Inflammatory Bowel Disease, type 1 diabetes, multiple sclerosis and a skin disease sometimes confused with psoriasis, atopic dermatitis.
A tendency to develop psoriasis may be inherited. A child with one parent with psoriasis has a 1 in 4 chance of developing psoriasis.
Researchers suspect that psoriasis occurs due to a combination of genetic and environmental factors. Someone with psoriasis may have an inherited tendency towards autoimmune or inflammatory diseases, but the disease only develops when there is a trigger such as infections, certain drugs, injury or stress.
Most people have their first outbreak between ages of 15 and 35, although it can appear at any age. About a quarter of young people report that their psoriasis first developed after an infection, such as a strep throat.
See Living Well with Psoriasis for tips on recognizing your triggers and how to deal with them.
Common Triggers
Common triggers for psoriasis and flare-ups of psoriasis are:
- Stress: has been shown to trigger psoriasis or to aggravate it.
- Injury to the skin: When psoriasis appears in areas of the skin that have been injured (sunburn, scratches, vaccination), it is referred to as “Koebner (KEB-ner) phenomenon.” If caught very early, this can be treated.
- Infection: Streptococcal infections (such as a strep throat) may trigger a certain type of psoriasis, known as guttate psoriasis.
- Medication: Some medications have been found to trigger psoriasis or flare-up in some people.
- The psychiatric drug lithium
- Antimalarial medications (quinacrine, chloroquine and hydroxychloroquine)
- Some blood pressure medications, such as the beta blocker propranolol
- The heart medication quinidine
- The arthritis mediation indomethacin
- The withdrawal of some steroid medications (corticosteroids)
If you think your medication is affecting your psoriasis, talk to your doctor, nurse practitioner or pharmacist before making any changes.
