Skin cancer types: Squamous cell carcinoma causes
What causes squamous cell skin cancer?
People usually develop this skin cancer because ultraviolet (UV) light has badly damaged their skin. Most UV light comes from:
Indoor tanning equipment (such as tanning beds and sunlamps)
Sun protection can greatly reduce your risk of developing skin cancer
The American Academy of Dermatology recommends seeking shade, wearing sun-protective clothing, and applying a sunscreen that offers broad-spectrum protection, water resistance, and an SPF of 30 or higher to all skin not covered by clothing.
How can UV light play a role in causing skin cancer?
Every time UV light hits our skin, it can damage some of the DNA inside our skin's cells. This happens every time we:
Spend time in the sun without sun protection
Use indoor tanning equipment
The body tries to repair this damage. When the body can no longer repair all the damage, changes called mutations develop in our skin’s cells. The mutated cells, which are cancer cells, can multiple quickly. As these cells pile up, a tumor develops.
When a tumor forms in skin cells called squamous cells, we get squamous cell skin cancer. These cells are found in the outermost layer of our skin, which is called the epidermis. The following picture shows you where these cells live.
Do some people have a higher risk of developing squamous cell carcinoma skin cancer?
Yes. The key risk factors for getting this skin cancer are listed below. A risk factor is anything that increases your risk of developing a disease.
UV damage to your skin caused by the sun or tanning beds. This is the most common contributing factor. Indoor tanning can increase your risk of developing squamous cell skin cancer by 58%1.
Fair skin, light-colored eyes, or naturally red or blond hair. If you have any of these traits, your skin is more easily damaged by the sun.
Sunburns. If you’ve had blistering sunburns, especially in your youth, you have a higher risk of developing squamous cell skin cancer.
Actinic keratoses (AKs). These are precancerous growths on your skin, which are caused by the sun or indoor tanning. Having an AK increases your risk of developing squamous cell skin cancer because an AK can progress and turn into this type of skin cancer. While not every AK turns into skin cancer, dermatologists recommend treating AKs to prevent this.
Sunny region. Living in an area that’s warm and gets plenty of sun year-round, such as Florida or California, increases your risk.
High altitude. Living at a high altitude also increases your risk.
Previous skin cancer. Having had skin cancer increases your risk of developing more skin cancers.
Medication taken to prevent your body from rejecting a transplanted organ. If you have a transplanted organ, such as a kidney, heart, or lung, you have a significantly increased risk of developing squamous cell skin cancer. Being under a dermatologist’s care can help you manage this increased risk.
HPV infection. Squamous cell skin cancer can develop under a nail, on the genitals, or inside the anus. Researchers have found that in these areas, squamous cell carcinoma is often accompanied by an HPV (human papillomavirus) infection.
Skin injury, such as a burn. Have you burned your skin badly? If so, you have a higher risk of developing skin cancer on the skin that was burned. Skin cancer can also develop in scar tissue that forms after a serious burn or other injury. The skin cancer that most commonly forms where skin has been badly burned is squamous cell skin cancer, which tends to appear years after the injury.
If you seriously injure a fingernail or toenail, this skin cancer may develop under a nail.
Exposure to arsenic. People who have high levels of arsenic in their drinking water or food have a greater risk of developing squamous cell skin cancer. As many pesticides contain arsenic, people who spend a lot of time around pesticides also have an increased risk.
Cigarette smoking. Some studies suggest that smokers develop this skin cancer at an earlier age than do people who don’t smoke or have never smoked.
HIV. In looking at medical records, Danish researchers found that people who are HIV positive have a higher risk of developing the most common types of skin cancer, including squamous cell skin cancer. In this study, the risk of developing this cancer was 5.40% higher in people who were HIV positive than in people who did not have HIV.2
Weakened immune system. Our immune system helps defend against cancer, so when something weakens it, we have a greater risk of developing skin cancer. Some medications, such as those that help prevent the body from rejecting a transplanted organ, weaken the immune system. Diseases such as leukemia, also weaken the immune system.
Xeroderma pigmentosum or similar inherited disease. Some people are born with a medical condition called xeroderma pigmentosum (XP). If you have XP, your body cannot repair any of the damage caused by UV light, so your risk of developing skin cancer skyrockets. It’s estimated that XP can raise the risk of getting skin cancer 10,000-fold.
While having one or more of these risk factors increases your risk of developing it, some people who get this skin cancer don’t seem to have any risk factors. People of all colors get this skin cancer, including people of African, Asian, and Latin descent.
If you find a spot on the skin that is growing, bleeding, or changing in any way, see a board-certified dermatologist to find out what it is. No one knows your skin better than a board-certified dermatologist.
You’ll find out how dermatologists diagnose and treat this skin cancer at, Squamous cell carcinoma: Diagnosis and treatment.
1 American Academy of Dermatology. Indoor tanning fact sheet. Last updated 6/21/22. Last accessed 4/1/23.
2Omland SH, Ahlstrom MG, et al. “Risk of skin cancer in patients with HIV: A Danish nationwide cohort study.” J Am Acad Dermatol 2018;79:689-95.
Anadolu-Brasie R, Patel AR, et al., “Squamous cell carcinoma of the skin.” In: Nouri K, et al. Skin Cancer. McGraw Hill Medical, China, 2008: 86-114.
Nadhan KS, Chung CL, et al. “Risk factors for keratinocyte carcinoma skin cancer in nonwhite individuals: A retrospective analysis.” J Am Acad Dermatol (2019), doi: https://doi.org/10.1016/j.jaad.2019.01.038.
Haley CT, Mui UN, et al. “Human oncoviruses: Mucocutaneous manifestations, pathogenesis, therapeutics, and prevention (Part I: Papillomaviruses and Merkel cell polyomavirus).” J Am Acad Dermatol (2018), doi: https:// doi.org/10.1016/j.jaad.2018.09.062.
Omland SH, Ahlstrom MG, et al. “Risk of skin cancer in patients with HIV: A Danish nationwide cohort study.” J Am Acad Dermatol 2018;79:689-95.
Que SKT, Zwald F, et al. “Cutaneous squamous cell carcinoma Incidence, risk factors, diagnosis, and staging.” J Am Acad Dermatol 2018;78:237-47.
Paula Ludmann, MS
Elan M. Newman, MD, FAAD
Rajiv Nijhawan, MD, FAAD
Brittany Oliver, MD, FAAD
Last updated: 4/28/23