Most skin cancer is caused by ultraviolet (UV) light damaging the DNA in skin cells. The main source of UV light is sunlight.

Sunlight contains three types of UV light:

• ultraviolet A (UVA)
• ultraviolet B (UVB)
• ultraviolet C (UVC)

UVC is filtered out by the Earth's atmosphere, but UVA and UVB damage skin over time, making it more likely for skin cancers to develop. UVB is thought to be the main cause of skin cancer.

Artificial sources of light, such as sunlamps and tanning beds, also increase your risk of developing skin cancer.

Repeated sunburn, either by the sun or artificial sources of light, increases the risk of melanoma in people of all ages.

Moles

You are at an increased risk of melanoma if you have lots of moles on your body, especially if they are large (over 5mm) or unusually shaped.

Having just one unusually shaped or very large mole increases your risk of melanoma by 60%.

For this reason, it's important to monitor moles for changes and avoid exposing them to the sun.

Family history

Research suggests that if you have two or more close relatives who have had non-melanoma skin cancer, your chances of developing the condition may be increased.

Increased risk

Certain things are believed to increase your chances of developing all types of skin cancer, including:

• pale skin that does not tan easily
• red or blonde hair
• blue eyes
• older age
• a large number of freckles
• an area of skin previously damaged by burning or radiotherapy treatment
• a condition that suppresses your immune system – such as HIV
• medicines that suppress your immune system (immunosuppressants) – commonly used after organ transplants
• exposure to certain chemicals – such as creosote and arsenic
• a previous diagnosis of skin cancer

Want to know more?

• Cancer Research UK: Melanoma risks and causes.