What is Solar Keratosis?
Solar Keratosis are also known as Sunspots. These rough scaly lesions on the backs of hands & forearms, face & forehead are very common in Australia! Detecting a solar keratosis is a very common outcome of a routine appointment at a Skin Cancer Clinic appointment.
Aren’t Sunspots normal?
Sunspots affect around 80% of people by the age of 60¹. Sunspots are normal-unhealthy rather than normal-healthy, but they do matter. Solar Keratosis is important for these three reasons:
- The presence of Solar Keratosis indicates significant exposure to past ultraviolet light radiation and a higher risk of skin cancer in general.
- Solar Keratosis may develop into an important type of skin cancer: SCC (Squamous Cell Carcinoma). Indeed, Solar Keratosis is an intraepidermal neoplasia and is one end of a continuous spectrum – from Solar keratosis to IEC (Intraepithelial Carcinoma) to SCC.
- Solar Keratosis may appear similar to skin cancers – particularly IEC. Pigmented Solar Keratosis may appear similar to Melanoma.
Because of the risk of transition of Solar Keratosis to Squamous cell carcinoma, areas of solar keratosis are therefore generally treated. The precise risk of a specific untreated Solar Keratosis developing into SCC is not known for certain. One figure from a study suggests that there is a 10% chance that a person with 7 to 8 untreated Solar Keratoses will go onto to develop one SCC within 10 years. Research suggests that 60 to 80% of SCC arises from solar keratosis.
Some Solar Keratoses may go away on their own without any treatment other than good regular sun protection.
What does a Solar Keratosis look like?
The typical solar keratosis will be a red flat scaly area on a sun exposed area. Another way to think of them is a rough area of UV-damaged fair skin. They are often felt better than seen. They are usually less than 1cm in diameter although they may be grouped together as an almost continuous area of “field change.”
The appearances can vary hugely. There are different subtypes depending on their clinical appearance:
Classic Solar Keratosis (as described above – flat, scaly and red). Need to differentiate from an IEC.
Hypertrophic Solar Keratosis – These are raised from the skin (sometimes markedly raised) and covered with a thick scale on a red base. These can look similar to SCC.
Cutaneous horn – These are thin hard lesions that project up from the skin and are quite firm and often dark. Hence the term “horn” which may also be caused by SCC or a viral wart. See example.
Pigmented Solar Keratosis: found most commonly on the face and can look like a melanoma.
Actinic Cheilitis: Solar Keratosis on the lips. More common on the lower lips.
A dermatoscope may be needed to examine the lesion closely to help confirm that the lesion is a Solar Keratosis and not a skin cancer or alternative diagnosis. When there is doubt then a biopsy will be required.