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Southern Cross Medical Library

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Psoriasis – causes, symptoms, diagnosis, treatment

Psoriasis is a chronic inflammatory disease of the skin. Characteristic symptoms are thick, red skin, with flaky, silver-white patches. These patches can be small and may or may not be itchy and sore. More severe cases can cover large areas of the body and have a major impact on quality of life. The aim of treatment is to minimise symptoms and prevent infection of the skin.

Psoriasis is a common and often life-long condition, which may affect as many as one in 50 adults in New Zealand. Anyone can get psoriasis, but it is more likely to occur in people aged between 15 and 35 years. It is not contagious, i.e. it cannot be caught from or spread to another person. There are several different types of psoriasis, each with its own distinctive appearance. Some people will develop stiff swollen joints in combination with their psoriasis – a condition known as psoriatic arthritis. The persistent visual, and sometimes disabling, nature of psoriasis can result in social, psychological, and economic consequences for people with the condition. Hence, it is important to seek effective treatment and support.

Causes and complications

The cause of psoriasis is not fully understood but it is thought to occur when environmental factors (or triggers) interact with the body’s immune system in people who have a genetic predisposition to the condition, i.e. people who inherit a specific type of gene. This interaction results in increased production of skin cells, leading to cells rapidly building up on the surface of the skin.  Environmental factors that can trigger psoriasis in susceptible people include: 

  • smoking
  • heavy alcohol consumption 
  • injury to the skin 
  • bacterial or viral infections, including sore throat and strep throat 
  • physical trauma 
  • emotional stress 
  • obesity 
  • certain medications, including blood pressure and antimalarial drugs. 

Possible complications resulting from psoriasis include skin infections (that can result from vigorous scratching), depression, stress, anxiety, heart disease, diabetes, and inflammatory bowel disease. In addition, psoriatic arthritis can lead to joint damage. 

Signs and symptoms

Psoriasis may appear anywhere on the body but will often affect the elbows, knees, scalp and lower back. For some people, psoriasis appears as a few spots of dandruff-like scaling that is more of a nuisance than anything else. In other people, it is a severe condition that is painful, disfiguring, and disabling.  Signs and symptoms of psoriasis vary depending on the type of psoriasis. They typically include one or more of the following:

  • red raised patches of skin covered with loose silvery scales (plaques) 
  • dry cracked skin, which may bleed itching, burning, and soreness 
  • thick, pitted or ridged nails 
  • swollen, painful, and stiff joints 
  • eye problems - conjunctivitis or blepharitis. 

Symptoms come and go in cycles of remission (disappearance) and flare-up (return) over a lifetime. 


Your doctor or skin specialist can usually diagnose psoriasis by taking a full medical history and examining your skin, scalp, and nails. In some cases your doctor may take a small sample of skin (biopsy) to determine the type of psoriasis and to rule out other skin conditions, such as eczema or fungal infection. X-rays may be taken if you have joint pain. 


There is no cure for psoriasis but many treatments that offer significant symptom relief are available.  A series, or sequence, of treatments is usually required as treatments that work well initially may lose their effectiveness over time.  There are three main types of treatment for psoriasis: 

1. Creams, ointments and shampoos

Most of the time psoriasis is treated by applying topical medications to reduce inflammation and itching, remove dead skin cells, and to slow the growth of skin cells. Topical treatments include:

  • corticosteroid creams and ointments 
  • creams or ointments that contain coal tar 
  • creams containing salicylic acid 
  • anti-dandruff shampoos 
  • vitamin A or vitamin D creams. 

2. Phototherapy 

Phototherapy, or light therapy, is a treatment involving exposing the skin to specific types of artificial ultraviolet light, which helps to slow the growth of skin cells and reduce scaling and inflammation. 

3. Medicines 

Systemic (whole body) medications used for treatment of psoriasis are drugs that suppress or modify the behaviour of the immune system. They are usually used only in people with moderate to severe forms of psoriasis. Oral drugs, such as methotrexate and cyclosporine, are usually tried first. Drugs called biologicals, such as adalimumab and infliximab, which are given by injection, are used when oral drugs no longer work.  People with mild psoriasis may self-treat their symptoms using over-the-counter corticosteroid creams and exposing the affected skin to small amounts of sunlight. Other forms of self-therapy that may help to improve the appearance and feel of affected skin include:

  • taking daily baths, adding bath oil, colloidal oatmeal, or Epsom salts
  • using moisturiser 
  • covering affected areas overnight 
  • exposing affected skin to small amounts of sunlight 
  • relaxation therapy 
  • eating healthy foods. 


There are no specific ways to prevent psoriasis. However, keeping your skin clean and moist and avoiding known trigger factors, if possible, may help to reduce the number of flare ups. 

Further information and support

Psoriasis Association Southland (NZ)
Phone: (03) 216 8662


Kupetsky E.A., Keller M. Psoriasis vulgaris: An evidence-based guide for primary care. J Am Board Fam Med. 2013;26(6):787-801. 
Meffert J. (2014). Psoriasis (Web Page). Medscape Reference. New York: WebMD LLC. [Accessed 14/02/14] 
Psoriasis Association Southland (2013). Psoriasis: Understood. Your guide to plaque psoriasis. Invercargill: Psoriasis Association Southland (NZ) 
PubMed Health (2012). Psoriasis (Web Page). Bethesda: U.S. National Library of Medicine. [Accessed 14/02/14]

Created February 2014


Go to our Medical Library Index Page to find information on other medical conditions.