How does skin cancer develop?

Actinic keratosis

  • An actinic keratosis lesion begins in the top layer of the skin – the epidermis. The epidermis is as thin as a pencil line, and it provides a protective layer of skin cells that your body continually sheds and regenerates.
  • Normally, skin cells within the epidermis develop in a controlled and orderly way. Usually, healthy new cells push older cells toward the skin surface, where they die and eventually are sloughed off.
  • When skin cells are damaged by UV radiation, changes occur in the skin‘s texture and colour, causing blotchiness and bumps or lesions.

Although some actinic keratosis lesions may spontaneously return to normal skin, it is important that they are detected and treated - left untreated they may develop into the more serious form, squamous cell carcinoma. The good news is that actinic keratosis lesions can be safely and effectively treated. 

Squamous cell carcinoma

  • The most frequent cause of squamous cell carcinoma is too much exposure to UV light which can cause certain cells (called keratinocytes) in the epidermis layer of the skin to grow out of control and to develop into a tumour.
  • They can also develop from an actinic keratosis lesion.
  • If treated early, squamous cell carcinoma is curable; but if left untreated the tumour can invade deeply and spread throughout the body.
  • So it is vitally important that you take measures to help prevent squamous cell carcinoma from developing.

Basal cell carcinoma

  • Basal cell carcinoma arises from cells in the basal layer or in the outer root sheath of the hair follicle.
  • One major risk factor for basal cell carcinoma is exposure to UV light, which can damage the DNA in the basal cells.
  • If left untreated the area will begin to open, bleed or crust over repeatedly.

Basal cell carcinomas grow slowly and rarely spread to other parts of the body. But if left untreated, they can severely damage the surrounding skin area. 


  • Melanoma develops when normal pigment producing skin cells called melanocytes become abnormal, grow uncontrollably, and invade surrounding tissues.
  • Usually only one melanoma develops at a time.
  • Although melanomas can begin in an existing mole or other skin growth, most start in unmarked skin.
  • If untreated, melanoma cells will spread throughout the body.
  • It is vitally important to detect melanoma as early as possible.
  • Exposure to UV light may be partly responsible for the development of melanomas.