Psoriasis is caused by the increased production and turnover of skin cells.

The skin has three layers, the outermost of which is called the epidermis. The bottom part (basal layer) of the epidermis produces skin cells called keratinocytes.

Keratinocytes are formed by the basal layer and move upwards to reach the outermost surface of the skin (horny layer of the epidermis / stratum corneum). They then die and are shed off. The basal layer thus continually produces new keratinocytes to replenish those that are shed in the outermost layer.

Normally, it takes about 28 days for a keratinocyte to be produced in the basal layer, move upwards and then be shed in the outer layer.

In psoriasis, this cycle only takes 3 to 7 days due to increased turnover of keratinocytes. Consequently, keratinocytes, which are not fully developed, accumulate on the outermost layer of epidermis. This causes the formation of psoriatic plaques that are raised, red and scaly.

Although the exact cause of the increased turnover of skin cells is not known, it is widely thought that psoriasis results from the body’s immune system attacking the skin. Specifically, T-cells (a type of white blood cell) are thought to release chemicals that cause inflammation of the skin.

Psoriasis generally causes patches of red, scaly skin that may be itchy and sore. These are known as plaques.

There are several types of psoriasis. Depending on the type of psoriasis you have, plaques affect different parts of the body and cause different symptoms.

Chronic plaque psoriasis

Chronic plaque psoriasis (also known as psoriasis vulgaris) is the most common form of psoriasis. It accounts for between 80 and 90% of all cases of psoriasis.

It causes circular or oval plaques that are red or pink in colour. The plaques are raised off the surface of the skin and are covered in flaky, white or silver scales. They may be itchy or sore.

Plaques are most commonly found on the elbows, knees, scalp and lower back. They also tend to affect the both sides of the body symmetrically, so, for example, plaques on the right elbow will be accompanied by plaques on the left elbow. Chronic plaque psoriasis very rarely affects the face.

– Scalp psoriasis

Sometimes chronic plaque psoriasis may exclusively affect the scalp. This is known as scalp psoriasis. The white or silvery scales appear similar to dandruff. Scalp psoriasis may affect the whole scalp or produce just a few isolated patches. In severe cases, scalp psoriasis can produce temporary hair loss in the affected areas of skin.

– Flexural psoriasis

Chronic plaque psoriasis may also affect skin creases (known as flexures), such as the armpits, groin, under the breasts and in skin folds. This is known as flexural or inverse psoriasis. In contrast to traditional chronic plaque psoriasis, flexural psoriasis produces smooth red patches of inflamed skin that do not have flaky white scales. It is thought that the moisture of skin creases prevents scales from forming. Flexural psoriasis is worsened by sweating and friction from skin rubbing.

Chronic plaque psoriasis is known as a ‘relapsing-remitting’ condition. This means people with the condition will experience flare-ups followed by periods where they are free from psoriasis. The frequency of flare-ups varies from person to person. In about a third of people, psoriasis will go away completely at some point in their lives.

Pustular psoriasis

Pustular psoriasis causes clusters of small, fluid filled blisters (called ‘pustules’) to form on the skin. Palmoplantar pustular psoriasis, which only affects the palms of the hands and soles of the feet, is the second most common form of psoriasis. In this form of the condition, the eventually develop into brown, scaly spots, before peeling off.

More rarely, a form of pustular psoriasis known as generalised pustular psoriasis can affect areas of the body beyond the palms and soles. This is a serious condition that often requires admission to a hospital to be treated.

Nail Psoriasis

The fingernails (and sometimes toenails) are affected in approximately half of people with any type of psoriasis. This is known as nail psoriasis. Typically the condition produces small indentations or ‘pits’ in the surface of the nail. The nail may become discoloured, with the area around the nailbed becoming orange or red. It is also possible for the nail to become loose and separate from the nailbed (known as onycholysis). In some cases, the nail can crumble.

Guttate Psoriasis

Guttate psoriasis typically follows 2-3 weeks after a bacterial throat infection and causes several small (less than 1cm) oval or circular plaques on the body. It may affect the chest, scalp, arms and legs.

In many people, guttate psoriasis lasts for a few weeks before resolving. In others, the condition may persist for 3-4 months. Once guttate psoriasis has resolved, there is a good chance it will not come back.

Erythrodermic psoriasis

Erythrodermic psoriasis is a rare form of psoriasis that causes redness of the skin all over the body. Individual plaques cannot be seen, but the skin may be scaly and also warm to touch.

Hospital treatment is required for erythrodermic psoriasis, as it can cause serious problems such as dehydration, heart failure and hypothermia.

Psoriasis can often be diagnosed on a simple examination of the skin. In order to assess the extent and severity of the psoriasis, your doctor will want to see all the psoriatic plaques on your body.

In some cases, a small sample of the skin may need to be taken. This is known as a skin biopsy. The sample is sent to a laboratory to be analysed under a microscope, which can help confirm a diagnosis.

If you have problems with your joints and are suspected of having psoriatic arthritis, your GP may refer you to see a rheumatologist. This may require further tests including blood tests and X-rays of the joints.

Referral to a dermatologist

In some cases, your GP may need to refer you on to see a dermatologist. You may be referred to a dermatologist in the event:

• the GP requires a second opinion on your condition
• the psoriasis is extensive, affecting more than 10% of your body
• your current treatment is ineffective
• psoriasis is severely affecting your nails

There is no permanent cure for psoriasis, but the condition can be well controlled. Treatments for psoriasis aim to reduce the occurrence of psoriatic plaques and prevent flare-ups. There are several types of treatment available, which can be broadly classified into:

• Topical treatments – creams, ointments and other medications that are applied directly to the skin. These are usually the first treatments used by doctors for mild-moderate psoriasis.

• Phototherapy – light therapy that involves exposing the skin to ultraviolet (UV) light.

• Systemic therapies – oral medications and injections that are used in severe psoriasis and affect the entire body.

Topical treatments

• Emollients

Emollients are creams and ointments that moisturise the skin. They can reduce the appearance and formation of scales, and may also soothe itching. They are suitable for mild psoriasis and are typically applied 3-4 times a day. Emollients can also improve the effectiveness of other topical treatments.

You can get emollients through a prescription from your GP or buy them over the counter at a pharmacy.

• Steroid creams and ointments

Steroid creams and ointments include steroid drugs such as beclametasone, which reduce inflammation and prevent the overproduction of skin cells. They are generally applied to the skin for short periods (under 4 weeks). Stronger steroids may only be applied for up to 2 weeks. The reason for this is that long-term use of steroids can cause side-effects such as thinning of the skin.

Although steroids are effective treatments, there is a risk in some people that, after treatment, the condition can come back more severely. GPs will avoid prescribing very strong steroids for this reason.

• Vitamin D analogues

Vitamin D analogues include medications such as calcipitriol, calcitriol and tacalcitol. They work by slowing down the production of skin cells (keratinocytes). People with psoriasis typically report a beneficial effect within two weeks of using the creams/ointments.

About 20% of people using vitamin D analogues experience redness, itching and soreness of the skin as a side-effect. It is also important not to exceed the recommended dose of vitamin D analogues, as it may interfere with your blood calcium levels.

GPs may often prescribe vitamin D analogues in combination with other topical treatments.

• Coal tar preparations

Coal tar is a viscous, heavy oil that is applied to skin. It has been used a treatment for a long time and shown to reduce inflammation and remove scales from psoriatic plaques. It is not known how coal tar produces these effects.

Coal tar comes in various forms, including: creams, ointments, lotions, bath additives, scalp treatments and shampoos. Some people may find coal tar to have an unpleasant odour and it can also stain clothes. It can also irritate the skin and cause it to become more sensitive to sunlight.

• Dithranol

Dithranol is typically used for people with a few psoriatic plaques that are nevertheless quite large. It causes plaques to resolve by slowing down production of new skin cells.

Short-contact dithranol treatment shows good results in psoriasis. This involves applying dithranol to the psoriatic plaques for between 5 and 60 minutes each day and then washing the medication off. The strength of dithranol is gradually increased over weeks.

Dithranol can irritate healthy skin and so must be carefully applied to plaques only. It can also temporarily stain the skin and permanently stain clothes and bathroom fittings.

•  Tazarotene

Tazarotene cream contains a drug based on Vitamin-A. It is applied directly to psoriatic plaques. In about 20% of people it can cause skin irritation, so care must be taken to avoid healthy skin.

Tazarotene is unsuitable for pregnant women as it has the potential to cause birth defects. The drug is rarely prescribed by GPs as the National Institute of Clinical Excellence (NICE) found a lack of evidence to support the use of tazarotene in psoriasis.

• Salicylic Acid

Salicylic acid is applied to the skin and helps to remove scales. It may also help other topical treatments better penetrate the skin. For this reason, it is often prescribed along with a steroid cream or coal tar. It may cause skin irritation in some people.

Phototherapy

Phototherapy involves exposing the skin to ultraviolet (UV) light using a special lamp. It is considered as a treatment for psoriasis when topical treatments have failed to be effective.

There are two types of phototherapy for psoriasis:

•  Narrow Band Ultraviolet B (UVB) phototherapy

Narrow band UVB phototherapy requires exposure to ultraviolet light for a few minutes. The treatment is normally undertaken 2 -3 times a week over a period of 6 – 8 weeks. Depending on resources, you will probably have to go to a hospital dermatology department to receive this treatment. UVB phototherapy may be combined with other topical treatments that sensitise the skin, such as coal tar or dithranol.

• Psoralen and Ultraviolet A (PUVA) phototherapy

In PUVA (Psoralen and Ultraviolet A), people with psoriasis take a medication called psoralen, before being exposed to the UV light. Psoralen sensitises the skin for treatment with UV light. It can be taken orally or applied to the skin as a cream or by soaking in a bath. The therapy is normally given 2-3 times a week every 2-4 weeks.

Long-term treatment with PUVA is not recommended as it increases the risk of skin cancer. It may also cause itchiness, nausea and a burning sensation in the skin.

Systemic treatments

Systemic treatments are used for severe, widespread psoriasis and psoriasis that has not responded to topical treatment or phototherapy. They are either oral medications or injections. The drugs used may be very effective in treating psoriasis but are limited by their serious side effects.

Systemic treatments may be divided into two groups:

• Non-biologic treatments
• Biologic treatments

– Non-biologic treatments

• Methotrexate

Methotrexate is known as a disease-modifying drug. It dampens down the immune system, thereby slowing the down the production of new skin cells and improving psoriasis. Methotrexate also helps with psoriatic arthritis. It is usually taken as an oral medication on a weekly basis. People taking the drug will notice an effect between 3 and 12 weeks.

Methotrexate can have many side effects, including: nausea, tiredness, diarrhoea and mouth ulcers. The drug also reduces the number of white blood cells. Accordingly, your doctor will arrange regular blood tests to ensure that the number of white blood cells doesn’t fall too low.

Long-term use of methotrexate can cause liver damage. The drug can also cause birth defects, so it is not used in pregnant women. Sexually active men and women on the drug are advised to use contraception.

• Ciclosporin

Ciclosporin is another immunosuppressant drug that dampens down the immune system. It is generally considered for the short-term treatment of psoriasis flare-ups. It is also used to treat palmopalmar pustular psoriasis.

The drug can affect blood pressure and kidney function, so doctors will need to monitor these regularly (kidney function is assessed with a blood test).

• Acitretin

Acitretin is a retinoid drug (related to Vitamin A) that is taken orally. A doctor may prescribe acitretin if you have severe psoriasis that hasn’t improved with other non-biologic systemic treatments. It is also useful in pustular psoriasis.

The drug can cause side effects, including dryness of the mouth and nasal passage. Rarely, it may cause liver problems. Acitretin may also cause birth defects so is not suitable during pregnancy and women should use contraception while taking the drug.

– Biologic treatments

Biologic drugs are protein-based drugs that target parts of the immune system. They are used to reduce inflammation in severe psoriasis that has not responded to other treatments.

There are 4 biologic drugs licensed for use in psoriasis. All have them have been shown to be safe and effective.

• Etanercept

Etanercept belongs to a class of drugs known as anti-TNF drugs. These drugs block the effect of an inflammatory molecule called TNF-alpha (tumour necrosis factor – alpha). Etanercept is given as an injection twice a week for a period up to 12 weeks. The injection comes a pre-filled syringe or a pen device. A doctor or nurse will instruct you how to administer the injection to yourself.

In 15% of people, it causes side effects such as soreness, redness and irritation of the skin around the injection site. The drug suppresses the immune system, so there is a small risk of developing serious infections such as tuberculosis. Accordingly, the doctor will need to take regular blood tests in order to monitor your immune system.

• Adalimumab

Adalimumab is another anti-TNF drug. It is injected once every two weeks for up to 16 weeks. Clinical trials have shown that, between 3 and 12 weeks, 68% of people with psoriasis report a benefit using adalimumab.

The drug can cause side effects such as a rash, swelling and itchiness around the injection site. These tend to subside within 3 to 5 days. There is also a risk of headaches.

Due to its immunosuppressive effects, adalimumab may increase the risk of serious infections. Doctors will therefore need to conduct regular blood tests to check your immune system function. Adalimumab is not suitable for pregnant women as it can cause birth defects. Sexually active women are advised to use contraception.

• Infliximab

Infliximab is another anti-TNF drug. It is given as an infusion into a vein and so requires that you go to hospital. The infusion typically takes over 2 hours. After the initial dose, treatment is then given at 2 weeks, 6 weeks and then every 8 weeks thereafter.

It takes between 4-8 weeks before people with psoriasis notice an improvement on the drug. Studies show that 75% of people respond well to the treatment.

About 5% of people develop an allergic reaction to infliximab, so doctors and nurses will monitor you closely on the first infusion. Infliximab can also cause headaches, colds and nausea.

As it suppresses the immune system, there is a risk of serious infections. A doctor will take an initial chest X-ray and regular blood tests to monitor your immune system.

• Ustekinumab

 Ustekinumab is a biologic drug that targets two inflammatory molecules, interleukin-12 and interleukin-23. It is given as an injection. The second injection is given 4 weeks after the first injection. It is then given once every 12 weeks thereafter, for as long as symptoms are controlled.

The drug takes between 3 and 12 weeks to cause improvements in psoriasis. Studies show that 67% of users have a good response to ustekinumab.

The injections may cause a rash, swelling and itchiness around the injection site. This normally subsides in 3 to 5 days. Due to its immunosuppressive effects, ustekinumab may increase the risk of serious infections. Doctors will therefore need to conduct regular blood tests to check your immune system function.

Family history

30% of people with psoriasis have a close family member who also has the condition. Studies of psoriasis in identical twins also suggest that some people may have a genetic susceptibility to develop psoriasis.

There are likely to be several genes that increase the likelihood of developing psoriasis. Possessing these genes, however, does not necessarily mean a person will develop the condition. It is possible that events in the environment (e.g. an infection or exposure to certain drugs) trigger psoriasis in people who are genetically susceptible to the condition.

For many people with psoriasis, the condition can flare up in response to certain events. These include:

• injury to the skin such as cuts, grazes, scratches or sunburn

• infections – certain infections, particularly throat infections caused by the Streptococcus spp. Bacterium, can cause flare-ups of both guttate and chronic plaque psoriasis.

• psychological stress – people report that stress can cause flare-ups of psoriasis, although this has been difficult to demonstrate in studies.

• smoking – smoking may both trigger psoriasis and aggravate an existing flare-up.

• alcohol – heavy drinking may cause flare-ups

• certain medications – several different medications may trigger psoriasis, including: beta-blockers (e.g. propranolol), anti-inflammatory drugs (e.g. ibuprofen), lithium, ACE inhibitors (e.g. captopril), anti-malarial drugs and some antibiotics.

• sunlight – many people report that sunlight improves their psoriasis, although it may aggravate in the condition in other people.

• hormonal changes – women with psoriasis are more likely to experience flare-ups of psoriasis in puberty, menopause and in the months after childbirth.

Psoriasis is associated with various other health conditions affecting other parts of the body. People with psoriasis are more likely to have the following conditions:

• Joint problems – between 7 and 40% of people with chronic plaque psoriasis will develop inflammation of the joints. This is a condition known as psoriatic arthritis. Typically it affects the joints in the fingers and toes, although it can affect other joints.

• Inflammatory bowel disease – psoriasis increases the risk of developing ulcerative colitis or Crohn’s disease (types of inflammatory bowel disease).

• Cardiovascular risk factors – people with psoriasis are more likely to have conditions which put them at higher risk of a heart attack or stroke. These so-called ‘cardiovascular risk factors’ include:
  • high blood pressure
  • type II diabetes or resistance to the effects of insulin (a hormone that controls blood sugar levels)
  • obesity (particularly fat around the abdomen – ‘abdominal obesity’)
  • high cholesterol and other blood fats

Collectively, this cluster of cardiovascular risk factors is known as the metabolic syndrome.

Avoid known triggers

It may be possible for you to avoid known triggers of your psoriasis. For example, if cuts to your skin cause flare-ups of your psoriasis, you may want to avoid unnecessary injury to the skin e.g. piercings, tattoos.

Cut down on smoking and alcohol

Both smoking and alcohol are known triggers of psoriasis. Smoking may also aggravate and existing flare-ups. People with psoriasis are also at increased risk of cardiovascular disease – smoking and heavy alcohol use can further increase this risk.

Eat a healthy diet and exercise regularly

This is recommended lifestyle advice for everyone. It is particularly apt for people with psoriasis, as they may at increased risk of diabetes and cardiovascular disease.

Adhere to treatments and get regular reviews

Taking your medication at the times and doses as prescribed leads to better treatment outcomes. Similarly, psoriasis is a long-term condition and getting regularly reviewed by healthcare professionals ensures the best outcomes.

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Kim, I. H., West, C. E., Kwatra, S. G., Feldman, S. R., & O’Neill, J. L. (2012). Comparative efficacy of biologics in psoriasis. American journal of clinical dermatology, 13(6), 365-374.

NICE CKS: Psoriasis (September 2014). Available online at: http://cks.nice.org.uk/psoriasis

Chronic Plaque Psoriasis. Patient.info- Professional Reference Article. Available online at: http://patient.info/doctor/chronic-plaque-psoriasis

Psoriasis. Patient.info. Available online at: http://patient.info/health/psoriasis-leaflet

Samarasekera, E., Sawyer, L., Parnham, J., Smith, C. H., & Guideline Development Group. (2012). Assessment and management of psoriasis: summary of NICE guidance. British Medical Journal, 345, e6712.