Skin Cancer—Types, Detection, and Risk Factors

Skin cancer is the most common type of cancer in the United States (US), and an estimated 1 in 5 Americans will develop skin cancer in their lifetime.1,2 Many types of skin cancer exist, and they can be categorized into two types: nonmelanoma skin cancer and melanoma.2 This article will provide information on the various types of skin cancer, including risk factors and how to spot them.

Nonmelanoma skin cancers

There are several types of nonmelanoma skin cancer, the most common being basal cell carcinoma (BCC) and squamous cell carcinoma (SCC). Merkel cell carcinoma (MCC) is a rare, aggressive type of nonmelanoma skin cancer.2

Basal cell carcinoma. BCC occurs in the basal cells of the epidermis (e.g., the top layer of the skin).3 BCC is most often caused by damage from ultraviolet (UV) radiation from sun exposure and/or indoor tanning. Some risk factors include having a lighter skin tone that burns/freckles easily and rarely tans, personal or family history of skin cancer,1,4,5 history of sunburns (especially blistering sunburns), weakened immune system, sun-sensitive skin conditions (e.g., xeroderma pigmentosum), and undergoing dialysis.4

BCC often develops on sun-exposed areas, such as the face, head, and neck.3,5 The appearance of BCC lesions varies; they can appear as shiny bumps, open sores that do not heal, pink growths, red patches/irritated areas, and growths with rolled edges and/or central indentations.5,6 In skin of color, BCC lesions can be pigmented and appear as black, pearly, translucent growths; due to pigmentation, BCC can be more difficult to detect in skin of color.7 

BCC is a slow growing cancer that rarely spreads to other parts of the body, and most cases can be successfully treated, with a five-year survival rate of about 100 percent.5 However, left untreated, BCC can invade the bone or tissues beneath the skin. Having BCC increases the risk of developing another BCC lesion somewhere else, and lesions can recur in the same location if they are not removed completely.3,5,6  

Squamous cell carcinoma. SCC develops in the squamous cells of the epidermis.3 As with BCC, SCC is most often caused by damage from UV radiation.5,8 SCC shares many risk factors with BCC, including having a lighter skin tone, personal or family history of skin cancer, weakened immune system, and sun-sensitive skin conditions.9 Other risk factors include history of human papilloma virus (HPV) infection (particularly in the case of genital SCC),5,9 age over 50 years, male sex, chronic infections and skin inflammation, and precancerous skin conditions (e.g., actinic keratosis).9

Although SCC commonly develops in sun-exposed areas, it can also occur in scars, chronic skin sores, and the genital area.3 SCC lesions can appear as red or pink scaly patches, crusted or open sores, thick wart-like areas, or elevated growths with a central depression.5,8 There are no notable differences in SCC appearance in skin of color, but SCC is more common in people of color than White people.7

SCC is more likely to grow and spread to other parts of the body than BCC, but it is rather uncommon, and most cases of SCC are found early and treated successfully. The five-year survival rate is 99 percent when caught early, though it might be lower among patients who are diagnosed at an advanced stage.5 Left untreated, SCC can become invasive and cause damage or disfigurement.8

Merkel cell carcinoma. MCC is a rare, aggressive form of skin cancer, also known as neuroendocrine carcinoma of the skin. Though rare, its incidence is increasing; in the US, rates of MCC rose by 95 percent from 2000 to 2013.2,10 Risk factors for MCC include exposure to UV radiation, weakened immune system, lighter skin tone, age older than 50 years, male sex, previous personal history of blood cancers or melanoma, and history of infection with Merkel cell polyomavirus.11

As with other nonmelanoma skin cancers, MCC frequently appears on sun-exposed areas. It often takes the form of a firm, painless, red, pink, or violet/blue lump that grows very quickly.11,12 MCC is much more common in White individuals than individuals of color,13 and although more research must be conducted to determine differences between White patients and patients of color, current research suggests that disease presentation is similar.14,15

Due to its propensity for fast growth, once MCC is diagnosed, patients often undergo testing to determine whether the cancer has metastasized. It typically spreads to the lymph nodes first, and it could also spread to other parts of the skin, bones, or organs. MCC commonly recurs after treatment.12 The five-year survival rate is 75 percent for tumors that have not spread (localized), 61 percent for tumors that have spread to nearby structures or lymph nodes (regional), and 24 percent for tumors that have spread to distant parts of the body, such as the liver or lungs (distant).16


Cutaneous melanoma is a rare, aggressive skin cancer that develops in melanocytes, the cells responsible for giving the skin its color, which are found in the lower part of the epidermis.17 The majority of melanoma cases are attributed to exposure to UV radiation.2 Factors that increase the risk of developing melanoma include having a lighter skin tone; history of blistering sunburns; presence of over 50 small moles, one or more large moles, or one or more atypical moles (e.g., jagged border, asymmetrical, multicolored); weakened immune system; family or personal history of skin cancer;17,18 and history of breast or thyroid cancer.18

About 70 to 80 percent of melanomas occur on apparently normal skin, while only 20 to 30 percent are found on existing moles.2 To spot melanoma, remember the ABCDEs:

Asymmetry: If you divide the lesion/mole in two, the two halves do not match.

Border: The border of the mole is uneven and might have scalloped, notched, or jagged edges.

Color: The mole is multiple shades of brown, tan, or black; as it grows, it might also contain red, blue, or white.

Diameter/Dark: The mole is 6mm/0.25 inches in diameter, about the size of a pencil eraser, or bigger. Some experts also recommend examining lesions that are darker than others.

Evolving: The mole changes shape, size, color, or elevation or develops a new symptoms, such as bleeding, crusting, or itching.19

Melanoma can also be spotted using the “Ugly Duckling” test. Most normal moles on the body resemble each other, so be on the lookout for an ugly duckling, or a mole that is notably different than the others. These ugly ducklings might be lighter, darker, bigger, or smaller than neighboring moles. Isolated moles should also be considered suspicious. Also, be careful of amelanotic melanomas, as these lesions lack melanin and thus appear red, pink, white, or colorless.19

Melanoma can present differently and be more easily overlooked in people of color. Acral melanoma, the most common form of melanoma among people of color, develops in places that are not typically exposed to the sun, such as the palms, soles of the feet, under the fingernails or toenails,19,20 mouth, or genitals.21 The ABCDEs and Ugly Duckling test are still helpful tools for determining melanoma in people of color. Another helpful tool is the alphabet of nail melanoma:

Age between 20 to 90 years; African American, Asian, Native American

Band of brown or black pigment in the nail; breadth greater than 3mm; border that is irregular or blurred

Change in size or growth of nail band; no change in irregularity despite treatment

Digit involved—nail melanoma is most common in thumbs; more suspicious if only one digit is pigmented; dominant hand involvement

Extension of brown or black pigment to side or base of nail

Family or personal history of melanoma or atypical moles.21

When diagnosed in early stages, melanoma is treatable, with a five-year survival rate of 99 percent; this fall to 68 percent when it spreads to the lymph nodes and 30 percent when it spreads to other organs.1 Melanoma can recur after treatment.17

Bottom Line

It is important to protect yourself against all types of skin cancer by practicing sun protective behaviors, such as applying sunscreen every day. Examine your skin frequently, and contact a dermatologist if you notice anything that seems suspicious. A healthy diet may also mitigate your risk of developing skin cancer. See sidebar “Preventative Nutrition in Skin Cancer” on adjacent page.


  1. American Academy of Dermatology. Skin cancer. Updated 22 Apr 2022. Accessed 14 Jul 2023.
  2. Skin Cancer Foundation. Skin cancer facts and statistics. Updated Jan 2023. Accessed 14 Jul 2023.
  3. American Cancer Society. What are basal and squamous cell skin cancers? Revised 26 Jul 2019. Accessed 14 Jul 2023.
  4. American Academy of Dermatology. Skin cancer types: basal call carcinoma causes. Updated 28 Apr 2023. Accessed 14 Jul 2023.
  5. Bibee K. Nonmelanoma skin cancer. Johns Hopkins Medicine. Accessed 14 Jul 2023.
  6. Skin Cancer Foundation. Basal cell carcinoma overview. Updated Jan 2022. Accessed 14 Jul 2023.
  7. Gupta AK, Bharadwaj M, Mehrotra R. Skin cancer concerns in people of color: risk factors and prevention. Asian Pac J Cancer Prev. 2016;17(12):5257–5264.
  8. Skin Cancer Foundation. Squamous cell carcinoma overview. Updated Mar 2023. Accessed 14 Jul 2023.
  9. Skin Cancer Foundation. Squamous cell carcinoma risk factors. Updated Feb 2022. Accessed 14 Jul 2023.
  10. American Academy of Dermatology. Skin cancer types: Merkel cell carcinoma overview. Accessed 14 Jul 2023.
  11. Scott JF. Merkel cell carcinoma. Johns Hopkins Medicine. Accessed 14 Jul 2023.
  12. National Cancer Institute. Merkel cell carcinoma treatment (PDQ®)—patient version. Updated 25 Jun 2021. Accessed 14 Jul 2023.
  13. Martin MR, Mohsin N, Vilasi S, et al. Challenges documenting racial disparities in Merkel cell carcinoma. Cancer Biol Ther. 2022;23(1):1–3.
  14. Smith T. Racial differences between Merkel cell carcinoma patient outcomes. 24 Mar 2023. HCP Live. Accessed 14 Jul 2023.
  15. Kadiri S, Aissa A, Berhili S, et al. Merkel cell carcinoma occurring in a black woman: a case report. J Med Case Rep. 2017;11(1):25. 
  16. American Cancer Society. Survival rates for Merkel cell carcinoma. Revised 1 Mar 2023. Accessed 14 Jul 2023.
  17. National Cancer Institute. Melanoma treatment (PDQ®)—patient version. Updated 30 Jun 2023. Accessed 14 Jul 2023.
  18. American Academy of Dermatology. Skin cancer types: melanoma causes. Accessed 14 Jul 2023.
  19. Skin Cancer Foundation. Melanoma warning signs. Updated Jan 2021. Accessed 14 Jul 2023.
  20. Melanoma Research Alliance. Melanoma and skin of color. Accessed 14 Jul 2023.
  21. Brennard M, Buster K. Melanoma. Skin of color society. Accessed 14 Jul 2023.   

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