• A precancerous lesion of the skin composed of atypical keratinocytes. It is characterized by the presence of thick, scaly patches of skin. Several histologic variants have been described, including atrophic, acantholytic, hypertrophic, proliferative, lichenoid, bowenoid, and pigmented variants.
  NCI
  U.S. National Cancer Institute, 2021
• A scaly, crusty lesion caused by damage from the ultraviolet radiation of the sun, with typical location on sun-exposed areas of the skin. Actinic keratosis lesions are often elevated, rough, and wartlike, and may be red, or occasionally tan, pink, or flesh-toned in color.
  Human Phenotype Ontology (HPO)
  The Human Phenotype Ontology Project, 2025
• A thick, scaly patch of skin that may become cancer. It usually forms on areas exposed to the sun, such as the face, scalp, back of the hands, or chest. It is most common in people with fair skin.
  NCI Dictionary of Cancer Terms
  U.S. National Cancer Institute, 2021
• Scaly pink or red-brown raised spots or patches on the skin caused by overexposure to the sun. Actinic keratosis may be a precursor to skin cancer.
  Harvard Dictionary of Health Terms
  Harvard Medical Publishing, 2011
• (keratosis, actinic) White or pink lesions on the arms, hands, face, or scalp that arise from sun-induced DNA DAMAGE to KERATINOCYTES in exposed areas. They are considered precursor lesions to superficial SQUAMOUS CELL CARCINOMA.
  NLM Medical Subject Headings
  U.S. National Library of Medicine, 2025
• Actinic keratosis (AK) is a UV light�induced lesion of the skin that may progress to invasive squamous cell carcinoma. It is by far the most common lesion with malignant potential to arise on the skin.
  Medscape
  WebMD, 2025
• An actinic keratosis (ak-TIN-ik ker-uh-TOE-sis) is a rough, scaly patch on your skin that develops from years of exposure to the sun. It's most commonly found on your face, lips, ears, back of your hands, forearms, scalp or neck.
  Mayo Clinic
  Mayo Foundation for Medical Education and Research, 2025
• Actinic keratosis (AK) lesions are skin-colored, yellowish, or erythematous, ill-defined, irregularly shaped, small, scaly macules or plaques localized in sun-exposed areas of the body. Typically, they occur in middle-aged or older men with light-colored skin and a history of chronic sun exposure. They have the potential to progress into...
  Epocrates
  Athenahealth, Inc., 2019