In most cases, the causes of cancer in children and young people are unknown.

While we don’t know for sure why some people develop cancer and others don’t, we do know that cancer isn’t contagious. You don’t catch it from people, and you can’t pass it on to others. It’s also important to understand that it is very unlikely that anything you or your child has done has caused their cancer.

It is possible that some cancers start before your child was born, when their cells are dividing rapidly while they are still in the womb. Cancers such as bone tumours in teenagers and young people may also be related to periods of fast growth when the cells are dividing rapidly, but their exact cause is not known.

It is thought that some cancers can occur after exposure to a type of virus – for example, the virus that causes glandular fever. Some types of the Human Papilloma Virus (HPV) have been linked to an increased risk of developing cervical cancer.

Certain genetic conditions can increase your child's risk of cancer. For example, people with Down’s syndrome have an increased risk of leukaemia. In some cases, your child may be slightly more likely to get certain types of cancer if their siblings or other family members have also been affected. Retinoblastoma, a rare form of eye cancer, is known to be inherited in 40% of cases. Brothers and sisters of someone with acute lymphoblastic leukaemia are at slightly increased risk of developing it themselves.

Some types of cancer treatments, such as radiotherapy and chemotherapy, do increase the risk of later developing another type of cancer. However, this is a rare occurrence – the risk is small compared to the risk of leaving your child's original cancer untreated.

Updated January 2015, next planned review 2017.