Psoriasis happens when your skin cells grow faster than usual.
Most people's skin cells grow, develop and flake off over a 3 to 4 week period.
But in people with psoriasis, this happens much faster, over 3 to 7 days.
Because of this, cells that are still new build up very fast on your skin. This causes flaky, crusty patches covered with scales.
Problems with your immune system
It's not known exactly why your skin grows faster when you have psoriasis. But it may be because of a problem with your immune system.
Your immune system helps keep your body safe from disease. It also helps fight infection.
One of the main types of cell used by your immune system is a T-cell. Your T-cells travel through your body to find and fight invading germs, such as bacteria. But in people with psoriasis, they start to attack healthy skin cells by mistake.
This is what causes the deepest layer of skin to make new skin cells that grow faster than usual. Your immune system then goes onto make more T-cells.
It's not known what exactly causes this problem with the immune system. But some genes and triggers in your surroundings may play a role.
Psoriasis runs in families. You may be more likely to get psoriasis if you have a close relative with it.
We do not know the exact role between genetics and psoriasis. But many genes are linked to psoriasis. It's likely that different mixes of genes may make you more likely to get it. But having these genes does not mean you will get psoriasis.
Your psoriasis may start or get worse because of a specific event (a trigger).
You may be able to stop a flare-up of your psoriasis if you know what your triggers are.
Common psoriasis triggers include:
- an injury to your skin, such as a cut, scrape, insect bite or sunburn (sometimes called the Koebner response)
- drinking too much alcohol
- hormonal changes - this happens mainly for women, for example during puberty and the menopause
- certain medicines - anti-inflammatory medicines, like ibuprofen, ACE inhibitors (for high blood pressure), lithium and some antimalarial medicines are triggers
- throat infections - some people get guttate psoriasis after a streptococcal throat infection
- other immune disorders, such as HIV, which cause psoriasis to flare up or appear for the first time
Psoriasis is not contagious, so you cannot spread it to another person.