Skin cancer refers to the uncontrolled growth of cancer cells in the skin. Left untreated, with certain classes of skin cancer, these cells can spread to other organs and tissues, such as lymph nodes and bone. Skin cancer is the most common cancer recorded in the United States, affecting 1 in 5 Americans during their lifetimes, according to the Skin Cancer Foundation.

How your skin Functions

Your skin operates as a barrier to protect your body against things like water loss, bacteria, and other harmful contaminants. The skin has two basic layers: a deeper, thicker layer (the dermis) and an outer layer (the epidermis). The epidermis has three main types of cells. The outermost layer is made up of squamous cells, which are constantly shedding and turning over. The deeper layer is known as the basal layer and is made of basal cells. Lastly, melanocytes are cells that make melanin, or the pigment that influences your skin color. These cells produce more melanin when you have more sun exposure, causing a tan. This is a protective mechanism by your body, and it’s actually a signal that you are getting sun damage.


The epidermis is in frequent contact with the environment. While it sheds skin cells regularly, it can still sustain damage from the sun, infection, or cuts and scrapes. The skin cells that remain are constantly multiplying to change the sloughed skin, and they can sometimes start to replicate or multiply excessively, creating a skin tumor that may either be benign or skin cancer.

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Actinic keratosis on the nose

Actinic keratoses are commonly found on sun-exposed areas, such as the face, back of the hands, and scalp. Photo: DermNet New Zealand

Actinic keratosis

Actinic Keratosis, also known as solar keratosis, seen as a red or pink rough patch of skin on sun-exposed areas of the body. This are caused by exposure to UV light in sunlight. This is the most frequent form of precancer and can develop into squamous cell carcinoma if left untreated.


Basal cell carcinoma

Basal cell carcinoma is also the most common form of skin cancer, comprising about 90 percent of all cases of skin cancer. Most common in the head and neck, basal cell carcinoma is a slow-growing cancer that scarcesly spreads to other parts of the body. It usually shows on skin as a raised, pearly or waxy pink bump, often having a dimple in the middle. It can also appear translucent with blood vessels near the skin’s surface.

Squamous cell carcinoma

Squamous cell carcinoma actally affects cells in the outer layer of the epidermis. It is typically more aggressive than basal cell carcinoma and can spread to other body parts if allowed untreated. It appears as red, scaly, and rough skin lesions, typically on sun-exposed areas such as the hands, head, neck, lips, and ears. Similar red patches may be squamous cell carcinoma in situ (Bowen’s disease), the earliest form of squamous cell cancer.


While overall less common than basal and squamous cell carcinoma, melanoma is by far the most dangerous, creating about 73 percent of all skin cancer-related deaths. It happens in the melanocytes, or skin cells that create pigment. While a mole is a benign collection of melanocytes that most people have, a melanoma can be suspected if a mole has:

  • Asymmetrical shape
  • Border irregularities
  • Color that isn’t consistent
  • Diameter larger than 6 millimeters
  • Evolving size or shape

The four major types of melanoma

  • superficial spreading melanoma: the most common type of melanoma; lesions are usually flat, irregular in shape, and has varying shades of black and brown; it can occur at any age
  • lentigo maligna melanoma: usually affects the elderly; involves large, flat, brownish lesions
  • nodular melanoma: can be dark blue, black, or reddish-blue, but may have no color at all; it usually starts as a raised patch
  • acral lentiginous melanoma: the least common type; typically affects the palms, soles of the feet, or under finger and toenails

Kaposi sarcoma

While not typically seen as a skin cancer, Kaposi sarcoma is another type of cancer that involves skin lesions that are brownish-red to blue in color and usually found on the legs and feet. It affects the cells that line blood vessels close to the skin. This cancer is caused by a type of herpes virus, typically in patients with weakened immune systems such as those with AIDS.

Who is at risk?

While there are many different types of skin cancers, most share the same risk factors, including:

  • prolonged exposure to UV rays found in sunlight
  • being over the age of 40
  • having a family history of skin cancers
  • having a fair complexion
  • having received an organ transplant

However, young people or those with a dark complexion can still develop skin cancer.

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