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Causes and prevention - Skin cancer (melanoma)

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

Sunlight contains 3 types of UV light:

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

UVA and UVB damage skin over time, making it more likely for skin cancers to develop. UVC is filtered out by the atmosphere so does not harm our skin.

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

Repeated sunburn increases the risk of melanoma in people of all ages.


You have a higher risk of melanoma if you have lots of moles on your body. The risk increases if they are large (over 6mm) or an unusual shape.


Check your moles for changes and avoid exposing them to intense sun

Other risk factors

You're also more likely to develop melanoma skin cancer if you have:

  • a close relative who's had melanoma skin cancer
  • fair skin that does not tan easily
  • red or blonde hair
  • blue eyes
  • a large number of freckles
  • been sunburnt often over years
  • used sunbeds
  • a weakened immune system, due to an illness or medication
  • a previous diagnosis of skin cancer

The risk of getting skin cancer also increases with age.

Preventing melanoma

It's not always possible to prevent melanoma skin cancer. But you can reduce your risk of getting it.

In the summer you need to be really careful, especially if you have white skin and a lot of moles.

What you can do to reduce your risk

Follow the SunSmart 5S rule: slip, slop, slap, seek and slide

  • Slip on clothing that covers your skin such as long sleeves, collared t-shirts.
  • Slop on broad spectrum (UVA/UVB) water-resistant sunscreen - use factor 30+ for adults and 50+ for children and reapply often.
  • Slap on a wide-brimmed hat to protect your face, ears and neck.
  • Slide on wraparound sunglasses with UV protection to protect your eyes.
  • Seek shade especially if outdoors between 11am and 3pm - and always use a sunshade on a child’s buggy.


  • do not use sunbeds

  • do not try to get a suntan

  • do not get sunburnt

Check the UV index

The UV index tells you how strong the sun’s UV rays are each day.

You need to protect your skin when the UV index is 3 or above.

In Ireland, UV is usually 3 or above from April to September, even when it is cloudy. UV is usually strongest between 11am and 3pm.

Check the UV index on Met Éireann

Checking your skin

Checking your skin for signs of skin cancer can help you get an early diagnosis. Treatment has a better chance of being successful when melanoma is found early.

How to check moles on your back

To check moles on your back or the backs of your legs:

  • go somewhere that is well lit and use a full-length mirror or hand mirror
  • ask a friend or family member to check your moles

Compare the moles to a photograph to see if they have changed.

Symptoms of melanoma and ABCDE of moles

Content supplied by the NHS and adapted for Ireland by the HSE

Page last reviewed: 5 July 2023
Next review due: 5 July 2026

This project has received funding from the Government of Ireland’s Sláintecare Integration Fund 2019 under Grant Agreement Number 123.