Southern Cross Medical Library

Southern Cross Medical Library

Psoriasis is a common inflammatory disease of the skin, which affects 2-3% of New Zealanders.

It is called an ‘autoimmune’ disease, which means it is due to a person’s immune/defence system turning in on the body and attacking 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 greatly affect quality of life. The aim of treatment is to minimise symptoms and prevent infection of the skin.

Psoriasis is often a life-long condition. Anyone can get psoriasis, but it is more likely to occur in people aged between 15 and 35 years and those aged between 50 and 60 years.

Psoriasis is not contagious, ie, 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 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 (tendency) to develop the condition, ie, 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
  • Obesity

Possible complications associated with psoriasis include skin infections (that result from vigorous scratching), depression, stress, anxiety, heart disease, obesity and inflammatory bowel disease (ulcerative colitis, Crohn's 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

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


A doctor or skin specialist (dermatologist) can usually diagnose psoriasis by taking a full medical history and examining your skin, scalp, and nails. In some cases, a small sample of skin may be taken (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
  • Retinoid (a form of vitamin A) or vitamin D gels and creams.

  • Calcineurin inhibitors

2. Phototherapy

Phototherapy, or light therapy, is a treatment involving exposing the skin to specific types of artificial ultraviolet light (UV), which helps to slow the growth of skin cells and reduce scaling and inflammation. Repeated rounds of phototherapy are often necessary.

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 only used in people with moderate to severe forms of psoriasis. 


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 (ointment-based moisturisers are best, and should be applied immediately after bathing or showering)
  • Covering affected areas overnight
  • Exposing affected skin to small amounts of sunlight
  • Relaxation therapy (to reduce stress)
  • 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. It may be beneficial to avoid alcohol, quit smoking, and avoid second-hand smoke. There is also evidence that weight loss can help in controlling psoriasis.


Kim, W.B., Jerome, D., Yeung, J. (2017). Diagnosis and management of psoriasis. Can Fam Physician. 2017;63(4):278–285
Habashy, J. (2020). Psoriasis (Web Page). Medscape Drugs and Diseases. New York, NY: WebMD LLC. [Accessed: 03/03/21]
Mayo Clinic (2020). Psoriasis (Web Page). Rochester, MN: Mayo Foundation for Medical Education and Research. [Accessed: 03/03/21]

Reviewed: March 2021

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

The purpose of the Southern Cross Medical Library is to provide information of a general nature to help you better understand certain medical conditions. Always seek specific medical advice for treatment appropriate to you. This information is not intended to relate specifically to insurance or healthcare services provided by Southern Cross.