Risk factors for melanoma skin cancer

A risk factor is something that increases the risk of developing cancer. It could be a behaviour, substance or condition. Most cancers are the result of many risk factors. The most important risk factor for melanoma skin canceris ultraviolet radiation (UVR) from the sun and indoor tanning.

The number of new cases of melanoma skin cancer has increased in both men and women over the past 30 years. More men than women develop it. The chance of developing melanoma skin cancer increases with age, but it is also found in adolescents and young adults (15 to 29 years of age).

Lentigo maligna is a very early form of skin cancer (called melanoma in situ). It is sometimes described as a precancerous condition of the skin. If lentigo maligna isn’t treated, it may become melanoma skin cancer that can grow into deeper layers of skin or surrounding tissue. Some of the risk factors for melanoma skin cancer may also cause lentigo maligna. Find out more about lentigo maligna.

Risk factors are generally listed in order from most to least important. But in most cases, it is impossible to rank them with absolute certainty.

Ultraviolet radiation (UVR)

Many moles

Atypical moles

Congenital melanocytic nevi

Familial atypical multiple mole melanoma (FAMMM) syndrome

Other hereditary conditions

Light-coloured skin, eyes and hair

Personal history of skin cancer

Family history of skin cancer

CDKN2A gene mutation

Weakened immune system

There is convincing evidence that the following factors increase your risk for melanoma skin cancer.

Being in contact with ultraviolet radiation (UVR) is the most important risk factor for developing skin cancer. The sun is the main source of UVR. Indoor tanning equipment, such as tanning beds and sun lamps, is also a source of UVR.

Having a tan means that your skin has been damaged by contact with UVR. UVR can cause sunburns, premature aging, cataracts and skin cancers.

Most cases of melanoma skin cancer are caused by contact with UVR from the sun. It could be from being in the sun on and off during your lifetime or being in the sun early in your life. People who have had at least one blistering sunburn as a child or teenager have a higher risk of developing melanoma later in life. The more sunburns you have had, the greater the risk of melanoma.

A mole (melanocytic nevus) is a bump or spot on the skin that is usually brown or pink and has a smooth and regular border. Moles are made up of a group of melanocytes (cells that give skin, hair and eyes their colour). Most people have a few moles.

Most moles are harmless. But you have a higher risk of developing melanoma skin cancer if you have many moles.

Atypical moles (dysplastic nevi) look different from normal moles. They tend to be larger than 6 mm, while normal moles are usually smaller than 6 mm. Atypical moles have an irregular (uneven) shape with undefined borders, but a normal mole is usually round. Atypical moles often have different colours in them, which can range from pink to dark brown. They can look like a melanoma skin cancer, but they are not cancerous.

Having atypical moles increases your risk of developing melanoma skin cancer. This risk increases with the more atypical moles you have.

Congenital melanocytic nevi are birthmarks or moles that are present at birth or develop shortly after. They may be classified as small (less than 1.5 cm), medium (1.5 to 19.9 cm) or large (covering more than 5% of the body in preteens or greater than 20 cm in teens or adults).

The larger the congenital melanocytic nevus, the greater the risk of developing melanoma skin cancer.

Familial atypical multiple mole melanoma (FAMMM) syndrome is a hereditary condition where a person has many moles (usually more than 50) that often look different from normal moles. A person with FAMMM also has one or more close relatives with melanoma.

People with FAMMM syndrome have a very high risk of developing melanoma skin cancer.

The following hereditary conditions can also increase the risk of developing melanoma skin cancer.

Xeroderma pigmentosum is a hereditary condition that affects the skin so it can’t repair sun damage. When someone has xeroderma pigmentosum, their skin changes colour and ages prematurely because it is very sensitive to UVR. They alsohave a high risk of developing melanoma and non-melanoma skin cancers.

Werner syndrome is an inherited condition that causes the skin to age prematurely. Werner syndrome is most common in people of Japanese ancestry. People with this condition have a higher risk of developing melanoma skin cancer.

Retinoblastoma is a type of eye cancer in children. Hereditary retinoblastoma is passed on from a parent to a child. It is caused by an inherited RB1 gene mutation. Children with hereditary retinoblastoma have a higher risk for melanoma later in life.

People with fair or light-coloured skin have a higher risk of developing melanoma skin cancer than people with other skin types. People with blonde or red hair and blue, green or grey eyes also have a higher risk of developing melanoma. Their risk is greater because people with these features have less melanin. Melanin is what gives colour to your skin, hair and eyes. Experts think that it also helps protect the skin from UVR. People with a fair or light-coloured skin who had very bad sunburns at an early age have the highest risk for melanoma skin cancer.

People with dark (brown or black) skin have a lower risk of developing melanoma. People with dark skin may be more likely to develop a rare type of melanoma called acral lentiginous melanoma. This type of melanoma skin cancer occurs on areas not exposed to the sun, such as the soles of the feet or palms of the hands.

People who have already had melanoma skin cancer have a higher risk of developing another primary melanoma. Having had basal cell carcinoma (BCC) or squamous cell carcinoma (SCC) is also linked with a higher risk of developing another skin cancer, including melanoma.

Your risk of developing melanoma increases if one or more of your first-degree relatives has been diagnosed with melanoma. This may be due to family members having similar skin colour and sun exposure habits. It can also be due to similar genetic mutations, although this is rare.

Sometimes genes can change (mutate) so they increase the risk of developing cancer. These mutated genes can be passed down from parents to their children. If several family members have the same type of cancer, or if family members have related types of cancer, they might share an inherited gene mutation.

About 5% to 25% of families with a higher risk for melanoma have an inherited mutation in the CDKN2A gene. This gene is normally a suppressor gene, which means it helps control the growth of cancer cells. When there is a CDKN2A gene mutation, cancer may develop.

Find out more about genes and cancer.

People with a weakened immune system have a higher risk of developing melanoma skin cancer. The immune system can be weakened by certain diseases, such as infection with the human immunodeficiency virus (HIV). It can also be weakened by drugs that people need to take to suppress their immune system after an organ transplant.

The following factors have been linked with melanoma skin cancer, but there is not enough evidence to show for sure that they are risk factors. More research is needed to clarify the role of these factors for melanoma skin cancer.

• melanocortin 1 receptor (MC1R) gene mutation
• ionizing radiation
• working with products that contain a group of chemicals called polychlorinated biphenyls (PCBs)
• PUVA therapy
• tall adult height

To make the decisions that are right for you, ask your healthcare team questions about risks.