We don't know what causes most cases of myeloma but there are some known risk factors.
A risk factor is anything that increases your risk of getting a disease. Different cancers have different risk factors.
Even if you have one or more risk factor, it does not mean that you will definitely get cancer.
How common is myeloma?
Around 5,500 people in the UK are diagnosed with myeloma each year. That is 15 people every day.
As with most other cancers, the risk of myeloma increases as you get older and it is very rare in people under 40.
Monoclonal gammopathy of undetermined significance (MGUS)
Some people with myeloma already have a rare medical condition called monoclonal gammopathy of undetermined significance (MGUS).
MGUS means there are too many large protein molecules known as immunoglobulins in the blood. MGUS is often found by chance as it can show up in routine blood tests.
In most people MGUS doesn't cause any symptoms or need treatment.
Only a small number of people with MGUS develop myeloma. If you have MGUS, you usually see a specialist regularly for check ups.
Those with a parent, brother, sister, or child with myeloma or monoclonal gammopathy of unknown significance (MGUS) are 2 or 3 times as likely to develop myeloma or MGUS compared to people with no close family members with these illnesses.
People who take medicines to lower immunity after an organ transplant have an increased risk of myeloma compared to the general population. But the risk is still low. Less than 1 out of 100 people (1%) who have received an organ transplant develop myeloma.
People with HIV (human immunodeficiency virus) have an increased risk of myeloma.
Some medical conditions
An autoimmune condition called pernicious anaemia appears to increase the risk of myeloma and MGUS.
Other autoimmune conditions called ankylosing spondylitis, autoimmune haemolytic anaemia and systemic lupus erythematosis might also increase the risk of myeloma.
People with a rare genetic condition called Gaucher disease have an increased risk of myeloma. Gaucher disease causes a build up of fatty substances in certain organs of the body, such as the spleen and liver. This makes the organs larger and affects how well they work.
The fatty substances can also collect in the bones causing pain, weakness and breaks (fractures).
Evidence shows that people who are overweight or obese have an increased risk of myeloma compared to people with a healthy body weight.
Past exposure to radiation
People who have been exposed to high levels of radiation might have an increased risk of developing myeloma.
Myeloma is slightly more common in men than women. It's not clear why this is and there may be many factors involved including genetics and lifestyle.
Other possible causes
Stories about potential causes are often in the media and it isn’t always clear which ideas are supported by evidence. There might be things you have heard of that we haven’t included here. This is because either there is no evidence about them or it is less clear.