Addison's disease develops when the outer layer of your adrenal glands (your adrenal cortex) is damaged, reducing the levels of hormones it produces.
Problems with the immune system
In the UK, a problem with the immune system is the most common cause of Addison's disease, accounting for 70-90% of cases.
The immune system is your body’s defence against infection and disease. If you're ill, your immune system produces antibodies (a special type of protein that destroys disease-carrying organisms and toxins). These antibodies attack the cause of the illness.
However, if you develop a problem with your immune system, it can start to attack your own healthy tissues and organs. This is known as an autoimmune disorder.
Addison’s disease can develop if your immune system attacks your adrenal glands and severely damages your adrenal cortex. When 90% of the adrenal cortex is destroyed, your adrenal glands won't be able to produce enough of the steroid hormones cortisol and aldosterone. Once levels of these start decreasing, you'll experience symptoms of Addison’s disease.
It's not clear why some people develop this problem with their immune system, although it can run in families (see below).
Research has shown that some people with certain genes are more likely to develop autoimmune disorders.
It's not clear how these genes lead to Addison's disease and similar conditions, but it does mean your risk of developing Addison's disease is increased if you or a close family member have another autoimmune condition, such as:
- vitiligo – a chronic (long-term) condition that causes pale, white patches to develop on the skin
- type 1 diabetes – a chronic condition caused by too much glucose in the blood
- underactive thyroid gland (hypothyroidism)
Tuberculosis (TB) is the most common cause of Addison's disease worldwide, but is rare in the UK. TB is a bacterial infection that mostly affects the lungs, but can also spread to other parts of your body. It can cause Addison’s disease if it damages your adrenal glands.
Other possible causes of Addison’s disease include:
- infections – such as those linked to AIDS, or fungal infections
- a haemorrhage – very heavy bleeding into the adrenal glands, sometimes associated with meningitis or other types of severe sepsis
- cancer – if cancer cells from elsewhere in your body spread to your adrenal glands
- amyloidosis – a disease where amyloid, a protein produced by your bone marrow cells, builds up in your adrenal glands and damages them
- surgical removal of both adrenal glands (adrenalectomy) – for example, to remove a tumour
- adrenoleukodystrophy (ALD) – a rare, life-limiting, inherited condition affecting the adrenal glands and nerve cells in the brain that most often affects young boys
- certain treatments needed for Cushing's syndrome – a collection of symptoms caused by very high levels of cortisol in the body
Secondary adrenal insufficiency
The production of hormones from the adrenal gland can also be affected by damage to the pituitary gland (a pea-sized gland located below the brain), as the pituitary gland produces a hormone that stimulates the adrenal gland. This is a separate condition to Addison's disease, known as secondary adrenal insufficiency.
Secondary adrenal insufficiency can occur if your pituitary gland becomes damaged – for example, because of a tumour on the pituitary gland (known as pituitary adenomas).