Identify Cancerous, Non-Cancerous, and Pre-Cancerous Skin Lesions

Actinic keratosis, also called solar keratosis, is a precancerous skin lesion usually caused by too much sun exposure. It can also be caused by other factors such as radiation or arsenic exposure.

If left untreated, actinic keratoses can develop into a more invasive and potentially disfiguring skin cancer called squamous cell carcinoma. They appear predominantly on sun-exposed areas of the skin such as the face, neck, back of the hands and forearms, upper chest, and upper back. You can also develop keratoses along the rim of your ear.

Actinic keratosis is caused by cumulative skin damage from repeated exposure to ultraviolet light, including that found in sunshine. Over the years, the genetic material in your cells may become irreparably damaged and produce these pre-cancerous lesions. The lesions, like those seen here on the arm, can later become squamous cell carcinoma, a more invasive cancer.

Areas with high sun exposure such as the scalp (on bald individuals), forearms, face, and back of the neck are common sites for actinic keratoses.

These pre-malignant lesions ( the brown spots in the photo) are actinic keratoses. They are scaly and rough ​and can bleed. Here, they are shown on an ear, a typical, sun-exposed area of skin.

Actinic keratoses are rough and dry, which often makes them easier to feel than to see. They are initially flat and scaly on the surface and become slightly raised. Over time, they become hard and wart-like or gritty, rough, and sandpapery. They may develop a horn-like texture from overgrowth of skin keratin layer also known as hyperkeratosis.

Children may develop a benign lesion called a Spitz nevus. This type of mole is typically firm, raised, and pink or reddish-brown. It may be smooth or scaly and usually appears on the face, particularly the cheeks. It is not harmful but may be difficult to differentiate from melanoma, even for experts.

Although most moles are benign, certain types of moles carry a higher risk for melanoma. About 30 percent of the population has moles called dysplastic nevi, which are larger than ordinary moles—most are 5 mm across or larger, have irregular borders, and are various shades or colors. 

If you have dysplastic nevi plus a family history of melanoma, a syndrome known as FAMM, you have a high risk for developing melanoma at an early age, younger than 40. Similarly, giant congenital nevi (shown in the photo), are major risk factors for melanoma. In such cases, cancer usually appears by the time you are 10.

Psoriasis is an autoimmune skin condition that can increase your risk of developing squamous cell carcinoma. Studies conflict on whether it has any effect on melanoma. There is some evidence that long-term treatment for psoriasis using UVA radiation (PUVA) may increase your risk of melanoma.

Psoriasis appears on the skin as red, scaly patches of skin. These patches are often very itchy and dry. 

Keratoacanthomas are a low-grade subtype of squamous cell carcinoma. The majority occur in sun-exposed skin, usually on the hands or face.

They are typically skin-colored or slightly red when they first develop and can grow rapidly to 1 to 2 cm in size. Most will spontaneously get better within 1 year, but they almost always scar after healing.

Removal by surgery, or sometimes by radiation, is recommended. In cases not appropriate for excision, due to their size or location, keratoacanthomas may be treated with 5-fluorouracil, a type of medication used to treat cancer, either as a cream or by injection.