What causes melanoma? Sunlight!

Author: Vanessa Ngan, Staff Writer; Copy Editor: Clare Morrison; Chief Editor: Dr Amanda Oakley, Dermatologist, Hamilton, New Zealand, October 2013. About Melanoma is sponsored by the New Zealand Dermatological Society Incorporated.

Fun in the sun ruins our skin

In New Zealand, most melanomas are related in some way to ultraviolet radiation (UVR). UVR comes from the sun or from man-made sources such as sunbeds and tanning salons. UVR on the earth's surface is composed of short wavelength UVB and long wavelength UVA rays.

  • UVR damages skin cells and affects the immune system.
  • There is more UVR when the sun is overhead in the middle of the day and in summer.
  • There is also more UVR at high altitude or when the sun's rays are reflected from a white or shiny surface such as snow or beach sand.
  • Sunbeds produce a high level of UVR.
Sources of high exposure to UVR
Sun at the beachReflection from snowHigh altitudeArtificial UV
Exposed to the sun at the beach Reflection from snow increases exposure to UVR High altitude increases exposure to UVR Fluorescent lamp source of UVB

Ultraviolet radiation causes skin cancer

Damage from UVR begins as soon as the sun's rays reach our skin. UVR causes many visible and invisible changes in skin cells. These include:

Skin cells include keratinocytes, which produce keratin (a protein that is the building-block in skin, hair, nails and horn) and melanocytes, which produce melanin (a brown pigment). Melanin protects the skin by absorbing UVR before it can cause any damage.

Sun damage
SunburnActinic keratosesBasal cell carcinomaSquamous cell carcinoma
Sunburn Actinic keratoses Basal cell carcinoma Squamous cell carcinoma

Genetic factors

The main cause of melanoma is the sun, but genetic factors are also important. Genes determine:

  • The colour of our skin – dark skin is less likely to be damaged by UVR.
  • The number and type of moles – people with many moles or large, unusual moles are more likely to get melanoma.
  • Familial melanoma – some families are especially prone to melanoma.

Cancer can occur when genes are damaged.


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