Medical Encyclopaedia › Actinic keratosis (short definition)
In brief: Actinic keratosis is a change in the epidermis caused by many years of sun exposure. It is considered an early form or precursor of squamous cell carcinoma of the skin, a form of non-melanoma skin cancer. Most actinic keratoses do not progress, but some can turn into invasive skin cancer. They are therefore usually treated and checked regularly.
Causes and risk factors
The cause is UV radiation accumulated over decades, which damages the genetic material of skin cells. Mainly affected are areas that get a lot of sun: bald head and scalp, forehead, nose, ears, lower lip, backs of the hands and forearms. People with fair skin, older people, those who spend much work or leisure time outdoors and people with a permanently suppressed immune system, for example after an organ transplant, are at increased risk. Often, not just a single spot is affected but a whole sun-damaged field of skin with visible and not yet visible changes.
What does an actinic keratosis look like?
Typical are rough, scaly patches that can often be felt better than seen, like sandpaper. They can be skin-coloured, reddish or brownish and are usually a few millimetres to about a centimetre in size. Some become heavily keratinised. On the lower lip, the corresponding change appears as a scaly, rough lip (actinic cheilitis). Warning signs of progression to invasive cancer are nodular growth, hardening, pain, bleeding or rapid enlargement.
Diagnosis
The dermatologist usually recognises actinic keratoses by looking, feeling and examining with a dermatoscope. In the case of unclear, thickened or rapidly growing areas and if there is no response to treatment, a tissue sample is taken to rule out squamous cell carcinoma or other forms of skin cancer.
Treatment
The choice depends on the number, location and thickness of the lesions and on the wishes and state of health of those affected:
- Individual lesions: freezing with liquid nitrogen, removal with a curette or laser.
- Field therapy for larger sun-damaged areas: creams or solutions containing 5-fluorouracil, imiquimod or diclofenac, applied according to a schedule over weeks, or photodynamic therapy, in which a photosensitising cream is activated with light, also as a daylight variant.
Strong skin reactions with redness, crusting and burning are desired and temporary with many field therapies, but can be stressful. New actinic keratoses frequently develop, so repeated treatments are usual.
Prevention and occupational disease
The most important prevention is consistent sun protection: avoid the midday sun, seek shade, wear headgear protecting the neck and ears and clothing, and use sunscreen in addition. Anyone who has had actinic keratoses should have their skin checked regularly by a dermatologist. In Germany, people with statutory health insurance are entitled to skin cancer screening every two years from the age of 35. In people who work outdoors a lot, multiple actinic keratoses or squamous cell carcinoma can be recognised as an occupational disease (BK 5103); a suspicion should be reported to the statutory accident insurance. Treatment is covered by the health insurers.
Related terms in the encyclopaedia
Squamous cell carcinoma, Actinic cheilitis, UV radiation, Skin cancer screening, Photodynamic therapy, Fluorouracil, Imiquimod, Cryotherapy, Dermatoscopy
Sources
- Leitlinienprogramm Onkologie (AWMF, Deutsche Krebsgesellschaft, Deutsche Krebshilfe): S3-Leitlinie Aktinische Keratose und Plattenepithelkarzinom der Haut
- Leitlinienprogramm Onkologie: S3-Leitlinie Prävention von Hautkrebs
- Berufskrankheiten-Verordnung (BKV), Anlage 1, Nr. 5103: Plattenepithelkarzinome oder multiple aktinische Keratosen der Haut durch natürliche UV-Strahlung
- Gemeinsamer Bundesausschuss (G-BA): Krebsfrüherkennungs-Richtlinie – Hautkrebs-Screening
Note: This article is for general information and does not replace advice, diagnosis or treatment from a doctor, dentist or pharmacist. Last updated: October 2026.