Actinic keratosis (AK) is a pre-cancerous skin condition that appears as a dry, scaly sometimes hyperkeratotic lesion as a result of prolonged and repeated sun exposure. The typical AK lesion is a dry, scaly, skin-coloured, reddish-brown or yellowish-black lesion. The onset of AK is subtle and therefore often passes unnoticed for some time before diagnosis. AK lesions are usually found on chronically sun-exposed sites of the head and neck and the dorsa of the hands and forearms.

If left untreated, AKs can progress into thickened lesions and subsequently develop into invasive SCC. There is an emerging view that AK is an intra-epidermal malignancy and it exists in a continuum with squamous cell carcinoma (SCC), the second leading cause of skin cancer deaths in the US, so that AK will become SCC when dermal invasion occurs. The American Academy of Dermatology reports that 40% of all SCCs begin as AKs.

The majority of patients who have an AK lesion will have multiple lesions and further lesions will become clinically evident in the future. Thus an AK patient can face a lifetime of treatment. AKs are the most common pre-cancerous skin lesions worldwide and the treatment of AKs is the most common dermatologic procedure performed in the out-patient setting.

Based on a 2005 study by the Lewin Group, in the US each year there are 8.2 million office visits for the treatment of AK and AK affects more than 58 million Americans. The annual cost to the US healthcare system for the treatment and management of AK was US$1.1 billion in 2004.

The worldwide prevalence of AK is highest in Australia.