Stem cell or bone marrow transplants are complex treatments that carry a significant risk of serious complications.

It's important that you're aware of both the risks and possible benefits before treatment begins. You may wish to discuss them with your treatment team and your family.

Generally speaking, younger people who do not have any other serious conditions or those who receive transplants from a closely matched sibling are less likely to experience serious problems. People receiving transplants of their own stem cells (autologous transplants) are also less likely to experience serious side effects.

Sometimes, the transplanted cells recognise the recipient's cells as "foreign" and attack them. This is known as graft versus host disease (GvHD).

GvHD can happen within a few months of the transplant or develop several months, or occasionally a year or 2, later. The condition is usually mild but can sometimes be life-threatening.

Symptoms of GvHD can include:

• an itchy rash
• diarrhoea
• feeling and being sick
• a sensitive and dry mouth
• dry eyes
• dry, flaky skin
• shortness of breath
• joint pain
• yellowing of the whites of the eyes and the skin, although this may be less obvious on brown or black skin (jaundice)

Tell your treatment team if you develop these symptoms. GvHD can be treated with medicines that suppress your immune system and stop the transplanted stem cells attacking the rest of your body.

In preparation for a stem cell transplant, you'll need to have chemotherapy to destroy the damaged or diseased blood cells. These will eventually be replaced by the transplanted stem cells, although this process can take several weeks or more.

Until your body starts being able to produce healthy blood cells again, you may be at risk of:

• iron deficiency anaemia – a lack of red blood cells that can make you feel tired and short of breath; this may be treated with regular blood transfusions
• excessive bleeding or bruising caused by a lack of clotting cells called platelets; you may need transfusions of platelets if this is a problem
• infections – a lack of white blood cells and any immunosuppressant medicine you're taking will mean your body is not able to fight off infections

You'll need to stay in a special germ-free hospital room during the first few weeks after the transplant. After going home, you'll need to be careful about coming into contact with people with infections and take steps to prevent food poisoning.

You may also be given antibiotics to prevent or treat any bacterial infections.

Common side effects of chemotherapy include:

• feeling and being sick
• diarrhoea
• loss of appetite
• mouth ulcers
• tiredness
• rashes
• hair loss

These side effects are usually temporary and only last a few weeks. Hair usually grows back within a few months.

However, high-dose chemotherapy can also have some long-lasting effects, including permanent infertility, which affects most people who have the treatment.

Your treatment team will talk to you about the risk before treatment starts and the possible ways of having children in the future. This may include procedures to collect and freeze eggs or sperm, although this is not always possible.

Read more about fertility and chemotherapy from Cancer Research UK