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Causes - Skin cancer (melanoma)

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 most dangerous to the skin but is filtered out by the Earth's atmosphere. UVA and UVB damage pale skin over time, making it more likely for skin cancers to develop. UVB is thought to be the main cause of skin cancer. It isn't yet known if UVA also plays a role in causing melanoma.

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.


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

For this reason, it's important to 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
  • pale skin that doesn't tan easily
  • red or blonde hair
  • blue eyes
  • a large number of freckles
  • previously damaged your skin through sunburn or radiotherapy treatment
  • a condition that suppresses your immune system. This could be HIV, or you take medicines that suppress your immune system.
  • a previous diagnosis of skin cancer

The risk of developing skin cancer also increases with age.

Preventing melanoma

Melanoma isn't always preventable, but you can reduce your chances of developing it by avoiding getting sunburned (even going pink in the sun).

Most people get burnt while abroad on holiday or in Ireland in the summer while doing outdoor activities, such as gardening, sunbathing or playing sports.

In the summer you need to be really careful, particularly if you have pale skin and many moles. You can help protect yourself from sun damage by using sunscreen and dressing sensibly in the sun. Sunbeds and sunlamps should be avoided.

Regularly checking your skin can help lead to an early diagnosis and increase your chances of successful treatment.

Tips to reduce your risk

  • Know the UV index: When the UV index is 3 or above you need to protect your skin. In Ireland UV is usually 3 or above from April to September, even when it is cloudy. Stay safe by limiting time in the midday sun when UV is strongest, typically between the hours of 11:00am-3:00pm.
  • Slip on clothing: Cover skin as much as possible. Wear long sleeves. Wear collared t-shirts made from close-woven material that does not allow sunlight through.
  • Slop on broad-spectrum (UVA/UVB) sunscreen. It should have a sun protection factor (SPF) of at least 30+ for adults and 50+ for children. The sunscreen should have high UVA protection and is water resistant. Reapply regularly. No sunscreen can provide 100% protection. It should be used alongside other protective measures such as clothing and shade.
  • Slap on a wide brimmed hat: Protect your face, ears and neck.
  • Slide on sunglasses with UV protection: Guard your eyes from harm.
  • Shade: Use a sunshade on your buggy or pram, sit in cover of trees to avoid direct sunlight.
  • Never use a sunbed.
  • Do not deliberately try to get a suntan, and avoid getting a sunburn.

Checking your skin for signs of skin cancer can help lead to an early diagnosis. This can increase your chances of successful treatment.

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

Page last reviewed: 9 July 2019
Next review due: 9 July 2022

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