Psoriasis is a common skin disorder, which causes redness and irritation patches on the skin.

It is a chronic inflammatory disease primarily involving the skin and the joint. It can have systemic manifestations such as involvement of the cardiovascular system.

The cause of psoriasis is still not known but genetic and environmental factors are linked to this psoriatic skin disorder and a faulty immune system plays a key role in contracting it.


  • Psoriasis is very common.
  • As mentioned above, it is an autoimmune disease.
  • It is chronic and persistent.
  • There is no cure. Treatment is purely for relief from symptoms
  • It is not contagious. That means it does not spread by contact or by any other means.
  • Patches of psoriatic skin become dry, red, thickened, itchy, painful, and irritated. Silver-colored scales are formed on the skin.
  • During a lifetime, there are periods of remission followed by an aggravation of the condition.
  • Psoriasis can be associated with arthritis, which is called psoriatic arthritis. This is associated with pain and swelling of the joints and can be disabling.


Skin psoriasis is characterized by skin cells multiplying ten times faster than normal. The cells move from the lower layer of the epidermis (where they are formed) to the upper layer of the epidermis.

This uppermost layer consists of dead skin cells. This migration of skin cells normally takes 4 to 6 weeks. In psoriasis, this period is reduced to only 2 weeks.

As a result of this fast multiplication and fast migration of the skin cells, there is an accumulation of dead cells on the outermost surface of the skin. This excessive volume of dead skin cells on the outermost layer of the epidermis causes silver or whitish flakes of psoriasis on the skin.

Mode of distribution

Psoriatic skin patches can occur on any part of the body but are more commonly seen on the

  • arms,
  • legs,
  • trunk and
  • scalp
  • The knees and elbows are the most commonly affected.

Cost of treatment

The cost of systemic psoriasis therapy is rising very fast and the biology medicines can be costly. Annual approximate expenses for its treatment are given below.

How is the severity of psoriasis defined?

The National Psoriasis Foundation has laid down certain parameters for defining the intensity of this disease.

  • Mild psoriasis is defined when less than 3% of the body is affected.
  • 3% to 10% indicates moderate psoriasis.
  • More than 10% of the body indicates severe psoriasis. For clarity, the palm of one hand is roughly 1% of the body surface).

The degree of its severity is based on the following factors.

  • The proportion of the body area as indicated above
  • Progress of the disease symptoms such as the amount of redness and thickness of the plaques and scales
  • The effect of the disease on the patient’s life
  • The response of the disease to previous treatment.


There are several forms of psoriasis that have been identified though there is a belief that some more remain to be identified.

One type can transgress into another type or rarely, a person can suffer from more than one type at one time.

1. Plaque psoriasis

This is the most common type seen in 90% of psoriatic cases. It is characterized by raised and reddish skin patches or plaques covered with silvery or whitish scales. These plaques are oval or round varying from one centimeter to many centimeters wide. They are itchy and at times painful.

They can occur anywhere on the body including the genitalia and the mucosa inside the mouth but are more commonly seen on the elbows, knees, and the trunk.

Depending on the severity, the plaques may be few or many and in severe cases, the skin on the joints may develop cracks, which can bleed. If scratched, these plaques become inflamed. This is referred to as the Koebner phenomenon.

2. Guttate psoriasis

This is the second most common type of psoriasis and is seen primarily in children and young adults below 30 years of age. With reference to its appearance, guttate comes from the Latin word gutta which means drop.

For this reason, it is also referred to as raindrop psoriasis. The onset of this type is often sudden and usually 2 to 3 weeks after a bout of a streptococcal throat infection or tonsillitis.

It is characterized by small sores, the size of drops, and covered by fine scales, that commonly occur on the trunk, arms, legs, and scalp. Guttate psoriasis often goes away without treatment after running its course for a few weeks. However, at times, it may persist and treatment then becomes necessary.

3. Pustular psoriasis

This is a less common form, characterized by well-defined raised pustules filled with pus. If widespread, it is called generalized pustular psoriasis, which is accompanied by fever with chills, itching, and fatigue.

It can also appear in small patches on the hands, fingertips, and/or feet. Its onset appears as red and tender skin, which very quickly develops into pus-filled blisters. The skin becomes very scaly. These blisters dry within a day or two and can recur after a few days or weeks.

Pustular psoriasis that attacks the fingertips is called Acrodermatitis continua. This causes severe pain and can cause permanent nail destruction.

4. Inverse psoriasis

This form is characterized by smooth, bright red inflamed skin patches occurring in the folds of the skin such as armpits, under the breast, in the groin, under the buttocks, and in the folds of the abdomen.

The aggravation of this type of psoriasis is caused by friction of the skin and the sweat in the skin folds.

Scales in this type of psoriasis are absent. Due to moistness by sweat in these skin folds, yeast, and fungi thrive and trigger its onset.

Overweight people are more susceptible to this type probably due to bigger areas under the skin folds and excessive sweating.

5. Erythrodermic or exfoliative psoriasis

Of all the types of psoriasis, this is the least common. This type can be serious and almost the whole skin of the body can be infected. It can be crippling and at times even fatal. The whole skin becomes red and inflamed.

There is a red peeling skin rash, which usually itches and causes burning. There may be a high fever with chills. It is triggered by sunburn, certain medicines such as steroids, or an existing psoriasis that is not being controlled.

6. Psoriasis of the scalp or seborrheic psoriasis

Scalp psoriasis presents as dry and red itching areas covered with silvery-white scales. This affects the scalp and at times may extend below the hairline on the forehead and even on the outer ear.

Excessive amounts of dead skin flakes are seen on the shoulder and the hair, especially after scratching the scalp giving an impression of severe dandruff.

The difference between seborrheic dermatitis and scalp psoriasis is that the scales of dead skin are greasy or oily in seborrheic dermatitis, while in scalp psoriasis, they are dry.

7. Psoriatic arthritis

This is the development of arthritis along with skin psoriasis. Joint symptoms may appear before, during, or after the skin psoriasis.

Joints commonly affected are those of the hands and feet, but any joint can get affected. Psoriatic arthritis lasts for a long time and often recurs. It is of five types.

Arthritis often improves when skin symptoms improve. Symptoms include swollen and painful joints, stiffness, and progressive joint damage, which can cause permanent joint deformity. There may be accompanying conjunctivitis.


Statistics for the prevalence of psoriasis in the United States and country-wise in the world are given below.

Facts and figures

  • Psoriasis is a very common condition.
  • Its incidence is seen at any age but more commonly between the age of 15 years and 25 years.
  • Children and adolescents can develop psoriasis, but the incidence is less. It occurs primarily in adults and men and women are equally affected.
  • It can peak two times. The first peak can occur between 20 to 30 years of age and the second between 50 to 60 years of age.
  • Psoriatic arthritis can develop at any age but you see it more commonly between the age of 30 to 50 years.
  • About 1/3rd of psoriasis patients have at least one relative with this condition.
  • A child is 10% more prone to develop psoriasis if one parent has it and this rate increases to 50% if both parents have it.
  • According to The National Psoriasis Foundation, about 10% to 30% of psoriasis patients develop psoriatic arthritis.
  • About 60% of patients with this condition miss an average of 26 days of work during one year due to this illness.
  • It is found that psoriasis is more prevalent in moderate to cold climates and less frequent in tropical climates.

Statistics for the United States

  • In the United States, about 2% to 3% of the population is affected. That translates roughly to 7.5 to 8 million people.
  • Caucasians (white people) have double the rate of psoriasis than African Americans. Prevalence among American Africans is 1.3 % compared to 2.5 % among Caucasians.

Worldwide statistics

  • Worldwide, about 125 million people are affected by psoriasis – that is 2% to 3% of the world population.
  • About 25% of people suffer from moderate to severe form.
  • 71% of children affected show a strong family history, thus showing a strong genetic component.

Statistics by country

Below are country-wise statistics of ten countries for psoriasis starting from the highest to lowest.

  • Scandinavia – 7 to 8%
  • Denmark – 5 to 6%
  • Germany – 4%
  • USA – 2 to 3%
  • Canada – 2 to 3%
  • Russia – 2 to 3%
  • Northern Europe – 2 to 3%
  • Great Britain – 2%
  • China – 0.37%
  • Kuwait – 0.11%

The incidence of psoriasis is highest in Northern Europe and so is the incidence of streptococcal infection. Aboriginals (Australia and the Arctic) and Native Americans show no prevalence. The genetic component is stronger rather than any contributing environmental factor.

In America, the whites show a higher prevalence, having migrated from Europe, while the black population shows a much-reduced incidence having migrated from West Africa, which has had a low incidence of psoriasis.