Causes of Pressure Sores
Pressure ulcers develop when sustained pressure is placed on a particular part of the body and interrupts the blood supply to that part of the body.

Blood contains oxygen and other nutrients that are needed to help keep tissue healthy. Without a constant blood supply, tissue damage occurs and the tissue will eventually die.

The lack of blood supply means that the skin no longer receives infection-fighting white blood cells. Once an ulcer has developed, it can become infected by bacteria.

People with normal mobility do not develop pressure ulcers as their body automatically makes hundreds of regular movements that prevent pressure building up on any part of their body.

For example, while you are asleep you may think you are lying still, but you may shift position up to 20 times a night.

The risk factors for pressure ulcers can be divided into one of two categories:

intrinsic risk factors - you have an underlying health condition or other factor that makes you more vulnerable to developing pressure ulcers
extrinsic risk factors - factors in your immediate environment that put you at risk of developing pressure ulcers
In some cases, a person may have both intrinsic and extrinsic risk factors, which are discussed in more detail below.

INTRİNSİC RİSK FACTORS
Intrinsic risk factors for pressure ulcers include:

mobility problems - anything that affects your ability to move some or all of your body
poor nutrition - for your skin to remain healthy it requires nutrients that can only be supplied by eating a nutritious diet
an underlying health condition, which disrupts your blood supply or makes your skin more vulnerable to injury and damage
being over 70 years old
urinary incontinence and/or bowel incontinence
serious mental health conditions
Mobility problems
Possible reasons for having a mobility problem are:

having a spinal cord injury that causes some or all of your limbs to be paralysed
brain damage caused by an event such as a stroke or severe injury which results in paralysis
having a condition that is causing progressive damage to the nerves your body uses to move parts of the body, such as Alzheimer's disease multiple sclerosis or parkinson's diseases
having severe pain that makes it difficult to move some or all of your body
having a fractured or broken bone
recovering from the effects of surgery
being in a coma
having a condition, such as rheumatoid arthritis that makes it difficult to move your joints and bones
Poor nutrition
Reasons that your diet may lack nutrition include:

anorexia nervosa - a mental health condition where a person has an unhealthy obsession with maintaining a low body weight

dehydration- you do not have enough fluids in your body

dysphagia - difficulty swallowing food

Health conditions
Health conditions that can make you more vulnerable to pressure ulcers include:

type 1 diabetes and type 2 diabetes - the high levels of blood sugar that is associated with diabetes can disrupt normal blood flow
peripheral arterial disease- the blood supply in the legs becomes restricted due to a build-up of fatty substances in the arteries of the legs
heart failure - previous damage to the heart means it is no longer able to pump enough blood around the body
kidney failure - the kidney loses most or all of its functions; this can lead to a build-up of dangerous toxins (poisons) in the blood, which can cause tissue damage
chronic obstructive pulmonary disease - a collection of lung diseases; the low levels of oxygen in the blood associated with COPD can make the skin more vulnerable to damage
Ageing skin
There are several reasons why ageing skin is more vulnerable to pressure ulcers. These include:

with age, the skin loses some of its elasticity (stretchiness), which makes it more vulnerable to damage
reduced blood flow to the skin due to the effects of ageing
the amount of fat under the skin tends to decrease as people get older
Incontinence
Both urinary incontinence (inability to control your bladder) and bowel incontinence (inability to control your bowels) can cause certain areas of the skin to become moist and vulnerable to infection. This can trigger pressure ulcers to form.

Mental health conditions
People with severe mental health conditions such as schizophrenia (a condition where people have problems telling the difference between reality and imagination) or severe depression have an increased risk of pressure ulcers for a number of reasons:

their diet tends to be poor
they often have other physical health conditions, such as diabetes or incontinence
they may neglect their personal hygiene, making their skin more vulnerable to injury and infection
EXTRİNSİC RİSK FACTORS
Extrinsic risk factors for pressure ulcers include:

pressure from a hard surface, such as a bed or wheelchair
pressure that is placed on the skin through involuntary muscle movements, such as muscle spasms
moisture, which can break down the outer layer of the skin (epidermis)
The time it takes for a pressure ulcer to form will depend on:

the amount of pressure
how vulnerable a person's skin is to damage
Grade three or four pressure ulcers can develop over short time periods. For example, in susceptible people, a full-thickness pressure ulcer can sometimes develop in just one or two hours. However, in some cases the damage will only become apparent a few days after the injury has occurred.

TYPES OF PRESSURE
There are three main types of pressure that can lead to the development of pressure ulcers.

These are:

interface pressure – the pressure of the body pressing the skin down onto a firm surface
shear – the pressure that occurs when layers of skin are forced to slide over one another or deeper layers of tissue; shear can occur when a person slides down or is pulled up out of a bed or wheelchair
friction – pressure caused by something, such as a mattress or clothing, rubbing against the surface of the skin