The first sign of skin cancer is usually a change in the skin, such as an emerging lump, a new mole, or alterations to an existing mole. Identifying any changes early can facilitate a prompt diagnosis of cancer, which may improve a person’s outlook.

There are many types of skin cancer, but they fall into two distinct categories: melanoma and non-melanoma. Melanoma is less common than non-melanoma but more dangerous.

This article looks at several types of melanoma and non-melanoma skin cancers, what causes them, and how they appear on the skin. It also discusses how to reduce the risk of developing skin cancer.

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Skin cancer is the most common form of cancer in the United States. The Skin Cancer Foundation states that 1 in 5 people in the U.S. will develop skin cancer before the age of 70 years.

When the skin becomes exposed to UV light, the rays can damage the DNA in its cells. Usually, this happens as a result of direct sunlight on bare skin.

If this process damages certain genes, they can cause abnormal cells to divide and grow uncontrollably. These cells can form cancerous growths.

There are two main types of skin cancer: non-melanoma and melanoma. Non-melanoma cancers usually form in the basal and squamous cells, which are both in the outermost layer of skin. Melanoma cancers only occur in a specific type of cells called melanocytes. These cells control skin pigmentation by producing melanin.

Although melanoma is much less common than other skin cancers, it is more dangerous because it can easily spread to other parts of the body. Due to this, timely identification and treatment are essential.

There are many types of non-melanoma skin cancer, but the two most common types are basal cell carcinoma and squamous cell carcinoma.

Basal cell carcinoma

Basal cells are those at the base of the epidermis, which is the outermost layer of the skin.

According to the American Cancer Society, basal cell carcinoma is the most form of common skin cancer. It accounts for about 80% of all non-melanoma skin cancers.

Although it is most common in people over the age of 50 years, it can also occur in younger people, especially those who have had a significant amount of sun exposure.

The appearance of basal cell carcinoma can vary among individuals. However, this cancer can present as:

  • an open sore that remains open for weeks
  • a sore that oozes, weeps, crusts over, or bleeds
  • a shiny, pearly bump
  • a sore with a sunken center

Squamous cell carcinoma

This type of carcinoma forms in the cells at the top of the epidermis.

The Skin Cancer Foundation says that doctors diagnose an estimated 1.8 million cases of squamous cell carcinoma in the U.S. every year.

Squamous cell carcinoma can look like:

  • a persistent open sore
  • a scaly, crusted patch that may bleed and will not resolve
  • a crusty, wart-like growth

Merkel cell carcinoma

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This rare and aggressive form of cancer is becoming more common.

According to estimates, cases of Merkel cell carcinoma almost doubled between 2000 and 2013. It currently accounts for about 3,000 new cases every year in the U.S.

Merkel cell carcinoma can present as:

  • a firm, shiny, painless lump
  • a round, raised lesion
  • a fast-growing bump

Learn more about Merkel cell carcinoma.

Although melanoma skin cancers are less common than non-melanoma ones, they are more dangerous.

There are four main types of melanoma skin cancers: superficial spreading melanoma, nodular melanoma, lentigo maligna melanoma, and acral lentiginous melanoma.

Superficial spreading melanoma

This is the most common form of melanoma. It can appear within an existing mole, or it can present as a new lesion on a person’s skin.

In females, it is more likely to occur on the legs, whereas in males, it is more common on the torso.

Superficial spreading melanoma may appear as:

  • a flat patch of discolored skin
  • a lesion with irregular shape
  • a growth that changes in size, shape, or color
  • a patch with undefined borders

Nodular melanoma

This is the most aggressive form of melanoma. It grows vertically down into the skin, which makes it particularly dangerous. As it grows rapidly, it is usually invasive at the point of diagnosis.

It accounts for more than 10% of all melanomas.

This type of melanoma is more common in males than females. It often appears on the head and neck.

Nodular melanoma can look like:

  • a raised, round lump
  • a bump that is painful and may bleed
  • a mushroom-like growth with a smooth or rough surface
  • a lump that is more than 6 millimeters (mm) across

Learn more about nodular melanoma.

Lentigo maligna melanoma

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This type of melanoma is closely linked to sun exposure. It is more common in older people and individuals who have had a lot of sun exposure, including those who work outdoors.

It usually appears on sun-damaged areas of skin, such as the face, ears, arms, and torso.

Lentigo maligna melanoma can look like:

  • flat patches of skin that resemble a large dark freckle
  • patches that change shape and grow
  • a patch that is irregular in color
  • a lesion that can be painful and bleed

Learn more about lentigo maligna melanoma.

Acral lentiginous melanoma

This is the most common form of melanoma in people with darker skin tones. It usually appears on the soles of the feet, the palms of the hands, and other hard-to-detect areas.

It can look like:

  • a patch that is darker than the surrounding skin
  • a lesion with an irregular, bumpy, warty surface
  • a lesion that bleeds

Learn more about acral lentiginous melanoma.

Most skin cancers develop due to repeated, unprotected exposure to UV radiation. Although this is usually from the sun, it can also come from other sources of UV radiation, such as tanning beds.

Researchers have also found that certain inherited genes can increase a person’s risk of getting skin cancer. Defects in tumor-suppressing genes, including TP53 and PTCH1/PTCH2, can make an individual more susceptible to cancer.

Similarly, having a family history of skin cancer can make a person more likely to develop it themself.

There is also a link between squamous cell carcinoma and some types of human papillomavirus (HPV). These viruses affect the proteins that regulate skin growth, making them grow uncontrollably and increasing a person’s cancer risk.

Certain types of skin cancer are more likely in people who:

  • are assigned male at birth
  • are older
  • have a history of skin cancer
  • have fair skin and light hair
  • have a weak immune system
  • have lots of moles

The most common sign of skin cancer is a change in the skin. This can be a new growth, an open sore that does not heal, or a change in an existing mole.

The Centers for Disease Control and Prevention (CDC) recommend using the A-B-C-D-E rule to identify a potential melanoma:

  • A — Asymmetrical: Does it have an irregular shape?
  • B — Border: Does it have an irregular or jagged border?
  • C — Color: Is its color uneven?
  • D — Diameter: Is it larger than a pea (about 6 mm)?
  • E — Evolving: Has it changed in any way over the last few weeks or months?

Yes, it can. However, it depends on the type of skin cancer and its stage.

Non-melanoma skin cancers are less likely to spread. Basal cell carcinoma usually does not migrate to other parts of the body, but there is a small chance that squamous cell cancer will do so.

Melanoma skin cancer spreads more readily than non-melanoma, making it more dangerous. It can spread to the lymph nodes and, from there, to other organs in the body.

Although there is no way to eliminate the risk of cancer, many skin cancers are linked to repeated sun exposure. Following sun safety guidance will likely reduce a person’s risk of developing skin cancer. People can help protect themselves by:

  • avoiding prolonged exposure when UV rays are at their strongest, which is typically between 10 a.m. and 4 p.m.
  • staying in the shade where possible
  • wearing protective clothing, such as a wide-brimmed hat and clothes that cover the arms and legs
  • wearing wraparound sunglasses that block UVA and UVB rays
  • using a broad-spectrum sunscreen with an SPF of at least 15
  • refraining from using tanning booths and sunlamps

Up to 1 in 5 people in the U.S. will develop skin cancer at some point in their life.

Doctors generally classify the different types as either non-melanoma or melanoma cancer. Non-melanoma is usually less dangerous and less likely to spread, whereas melanoma is more aggressive.

If a person knows the signs of skin cancer, they may be able to identify a potential lesion early and seek treatment. People who wish to reduce their risk of skin cancer should practice sun safety and avoid indoor tanning.