What is psoriasis?

What are the causes of psoriasis?

Is psoriasis a genetic condition?

What triggers psoriasis?

What is the function of the skin?

What is the epidermis?

What is the dermis?

How is the skin affected by psoriasis?

What are the causes of psoriasis?
It is not known for certain what causes psoriasis. However there are two factors that are thought to play some role: genetic predisposition and psoriasis triggers.

Is psoriasis a genetic condition?
Psoriasis often runs in families, although this is not a hard and fast rule. If members of your family have it, that doesn't mean you will automatically get it too.

In fact it is very difficult to predict who will get psoriasis, because the abnormalities that cause it are found within several different genes. Therefore, no single gene can be tested to see if a person is likely to develop psoriasis.

So while the pattern of inheritance is unpredictable, genetics does play some role and this means that psoriasis is more likely to develop in someone who has affected family members.

What triggers psoriasis?
If you are genetically predisposed to developing psoriasis, you may find that certain triggers activate the condition, although it is important to note that, in most cases, the specific triggers cannot be identified.
• Streptococcal infection: This infection is a common cause of sore throats and tonsillitis. It can be pinpointed as a specific trigger in some people with psoriasis, particularly in children and young adults.
• Sun exposure: The sun's UV rays actually help the vast majority of people with psoriasis. However, for a very small minority (less than 5%), sunlight can aggravate the condition. Sunburn may also cause psoriasis to flare up.
• Drug use: Some drugs are known to worsen pre-existing psoriasis. One such drug is lithium, which is commonly used in the treatment of manic depression. You may also find that if you have been using corticosteroid drugs or potent topical steroid creams on your skin and then suddenly stop using them, your psoriasis may flare up.
• Hormonal factors: With women, hormonal factors can vary greatly. The effect of pregnancy on psoriasis is very unpredictable. Peak onset also tends to be when the periods start during puberty.
• Psychological factors: Some people find that stress acts as a trigger. However this can work both ways. A person may find that having psoriasis causes them to get stressed.
• Skin trauma: Psoriasis may develop if the skin is injured. This is known as the Koebner phenomenon. It most commonly appears as a line in an operation scar or in a scratch. It may also appear in the spots of chickenpox. This type of psoriasis often heals on its own.

What is the function of the skin?
The skin is the body's largest organ, covering about two square metres. It has a number of functions:
• It acts as a barrier against bacteria, chemicals and radiation.
• It maintains fluid balance within the body by preventing the loss of fluid and vital body chemicals.
• It helps to maintain a stable body temperature.
• It contains nerve endings which allow you to feel things. The skin is made up of two layers, the epidermis and the dermis. The third layer in the illustration, the hypodermis, is not actually part of the skin but is the fally layer on which the skin sits.

What is the epidermis?
The epidermis is the outer layer of the skin. There are no blood vessels or nerves in this part of the skin. As a result, if you push a pin sideways through it, it will neither hurt nor bleed.

The epidermis is made up of cells called epithelial cells. There is a continuous movement of these cells towards the surface of the skin. This is due to cells in the deeper part of the epidermis constantly dividing and moving outwards. As a result, the skin is constantly renewing itself.

As they get nearer the surface of the skin, the cells die and flatten out to become part of the outer, horny layer. These dead cells (scales) in the horny layer are continuously shed from the surface (scaling). However, in normal skin you will probably not notice this because they are shed in such tiny pieces. It takes about four weeks from the time of dividing for the cells to travel to the surface of the skin.

The epidermis is supported by the dermis, which is found directly underneath it.

What is the dermis?
The dermis is a vast network of elastic fibres, blood vessels, nerve endings, hair follicles, collagen, hair roots and sweat and lymph glands.

The fibres found in the dermis give the skin its strength and elasticity. As we get older, our skin loses some of this elasticity and begins to sag and wrinkle.

As there are blood vessels and nerve endings in the dermis, if it is cut it will bleed and hurt. Deep damage to the dermis will also result in scarring.

How is the skin affected by psoriasis?
When a person has psoriasis, the epidermis renews itself much more rapidly than in normal skin, sometimes up to seven times as fast. This means that the cells don't have enough time to mature fully. As a result, the scaling which appears is visible, white and loose, and can be easily removed by scraping over the psoriasis plaque. (In normal skin, scaling isn't noticeable because the scale is so small, it is rarely seen).

The actual plaque appears scaly and sometimes silvery in colour, because it is packed with immature skin cells which have made their way to the skin's surface too quickly.

Plaques also tend to be red in colour because, with psoriasis, the blood vessels increase in number, which causes an increased blood flow resulting in the red appearance. With psoriasis, there is considerable inflammation of the skin.

Back to top of page

Back to Homepage

Have you any comments on this clinic?
Contact us at editor@irishhealth.com