Squamous Cell Carcinoma of the Skin: Symptoms, Causes, and Treatment Explained
Updated: 3 days ago
Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: October 17, 2026
Quick Answer: What is squamous cell carcinoma of the skin?
Squamous cell carcinoma of the skin is a common, usually treatable skin cancer that begins in squamous cells and often appears on sun-exposed areas like the scalp, hands, ears and lips as a firm bump, scaly sore or wartlike growth. UV radiation causes most cases. [1] Most are removed with minor surgery or topical medicine; few spread.
When to see a doctor
Make an appointment with a healthcare professional for a sore or scab that doesn't heal in about two months, or a flat patch of scaly skin that won't go away. [1] Seek prompt care for a growth that is growing quickly, bleeding, or very painful, and tell your doctor if you have a weakened immune system or have had skin cancer before.
What the research says
Daily sunscreen reduced squamous cell tumors in a randomized trial. In the Nambour trial of 1,621 adults in Queensland, Australia, people assigned to apply an SPF 15+ sunscreen daily to the head, neck, arms, and hands for 4.5 years developed fewer squamous cell tumors (1,115 vs 1,832 per 100,000; rate ratio 0.61; 95% CI, 0.46-0.81). The difference in the number of people developing a first squamous cell carcinoma was not statistically significant (rate ratio 0.88; 95% CI, 0.50-1.56) (Green et al., The Lancet, 1999) [3].
A weakened immune system raises the risk. A 2026 meta-analysis of 27 studies including 21,405 organ transplant recipients found that azathioprine, an immunosuppressant, was associated with a higher risk of non-melanoma skin cancer (odds ratio 1.83; 95% CI, 1.22-2.75), with a significant increase in squamous cell carcinoma risk specifically. The authors recommend closer skin cancer monitoring for these patients (Salehi et al., Cancer Reports, 2026) [4].
What Is Squamous Cell Carcinoma of the Skin?
Squamous cell carcinoma of the skin is a cancer that starts as a growth of cells on the skin. It begins in squamous cells, which make up the middle and outer layers of the skin. [1] It is one of the most common types of skin cancer.
It is usually not life-threatening. [1] But if it isn't treated, it can grow large or spread to other parts of the body, and its growth can cause serious complications. [1]
To see where it begins, it helps to know how the skin works. Skin cancer starts in the cells of the outer layer, the epidermis. As new cells move up, they become squamous cells. Squamous cell carcinoma starts in these cells, basal cell carcinoma (another common skin cancer) begins in the basal cells below them, and melanoma starts in pigment cells called melanocytes. For a look at a deadly look-alike, see our article on amelanotic melanoma.
Most squamous cell carcinomas are caused by too much UV radiation from sunlight or from tanning beds and lamps. [1] Protecting your skin from UV light lowers the risk of this and other skin cancers.
Where Does Squamous Cell Carcinoma Appear?
Squamous cell carcinoma most often appears on sun-exposed skin, such as the scalp, the backs of the hands, the ears and the lips. [1] But it can appear anywhere on the body, even inside the mouth, on the bottoms of the feet, or on the genitals. [1] See our guides to skin cancer on the ear and actinic cheilitis, a sun-related lip condition.
Skin tone context | Where it most often appears | Why |
|---|---|---|
People who sunburn easily | Areas that have had a lot of sun (scalp, hands, ears, lips) | UV exposure drives the cancer |
People with Black and brown skin | More often on skin not exposed to sun, such as the genitals | Different distribution than the sun-exposed pattern |
The risk is highest in people with blond or red hair, light-colored eyes, and skin that freckles or sunburns easily. [1] But anyone of any skin color can get squamous cell carcinoma.
What Are the Symptoms?
Squamous cell carcinoma of the skin may appear as a firm bump, a flat scaly sore, a rough patch on the lip or a sore that doesn't heal. [1]
A firm bump (nodule). It may be skin-colored or look pink, red, black, or brown, depending on skin color. [1]
A flat sore with a scaly crust. [1]
A new sore or raised area on an old scar or sore. [1]
A rough, scaly patch on the lip that may become an open sore. [1]
A sore or rough patch inside the mouth. [1]
A raised patch or wartlike sore on or in the anus or on the genitals. [1]
Not every patch or bump is cancer, but the rule that matters most is about healing: see a healthcare professional for a sore or scab that doesn't heal in about two months, or a flat scaly patch that won't go away. Because color varies with skin tone, check every area of your skin, including areas that are rarely in the sun.
What Causes Squamous Cell Carcinoma?
Squamous cell carcinoma occurs when squamous cells develop DNA changes, most often caused by UV radiation from sunlight, tanning lamps or tanning beds. [1] The changes tell the cells to multiply quickly and to keep living when healthy cells would die. [1] This produces too many cells, which can invade and destroy healthy tissue and, over time, break away and spread. [1]
UV radiation causes most of these DNA changes, whether from sunlight, tanning lamps, or tanning beds. [1] Skin cancers can also develop on skin that isn't usually in sunlight, so other factors, such as a condition that weakens the immune system, can add to the risk. [1] If you want to understand how sun damage develops, see our guide to sunburn.
What Raises Your Risk?
Risk factor | How it raises risk |
|---|---|
Skin that sunburns easily | Common in people with less melanin, which helps protect against UV. Highest risk with blond or red hair, light eyes, and freckles |
Too much sun | UV radiation from the sun increases risk |
Tanning beds | Tanning bed use increases risk |
History of sunburns | Blistering sunburns in childhood or the teen years raise adult risk; sunburns in adulthood also count |
Precancerous skin lesions | Actinic keratosis or Bowen disease can turn into skin cancer |
Previous skin cancer | Having had it once makes getting it again much more likely |
Weakened immune system | Leukemia, lymphoma, or immunosuppressive medicines (for example after an organ transplant) |
Xeroderma pigmentosum | A rare genetic disorder with extreme sun sensitivity |
HPV infection | Human papillomavirus, passed through sexual contact, increases risk. See our guide to |
Scars or long-lasting wounds | It can form in scars, burns, and sores that don't heal |
To learn more about HPV-related cancers, see our overview of oral HPV.
What Complications Can Occur?
Untreated, squamous cell carcinoma can destroy nearby healthy tissue, spread to lymph nodes or other organs, and, although it is not common, be fatal. [1] The risk of spread may be higher if the cancer grows very large or deep, involves mucous membranes such as the lips, or occurs in a person with a weakened immune system. [1]
How Can You Prevent It?
Most squamous cell carcinomas of the skin can be prevented. [1]
Avoid midday sun. In much of North America the sun's rays are strongest between about 10 a.m. and 3 p.m. [1] Plan outdoor activity at other times, even in winter or on cloudy days, and stay in the shade when you can. [1]
Wear sunscreen year-round. Use a broad-spectrum sunscreen with SPF 30 or higher, even on cloudy days. Apply it generously and reapply every two hours, or more often if you are swimming or sweating. [1]
Wear protective clothing. Dark, tightly woven clothes that cover arms and legs, a wide-brimmed hat that shades your face and ears, and sunglasses that block UVA and UVB rays.
Don't use tanning beds. They give off UV radiation and increase skin cancer risk. [1]
Check your skin often. Look for new growths and changes in moles, freckles, bumps, and birthmarks, including your scalp, the bottoms of your feet, between your toes, and your genital area, and report changes to your healthcare team. [1]
How Is Squamous Cell Carcinoma Diagnosed?
Diagnosis begins with a physical exam, in which a member of your healthcare team asks about your health history and examines your skin. [2] The next step is a biopsy: a tool is used to cut away, shave off, or punch out some or all of the unusual skin area. The sample is tested in a laboratory to find out whether it is cancer. [2]
How Is Squamous Cell Carcinoma Treated?
Most squamous cell carcinomas can be removed with minor surgery, and some with a medicine applied to the skin. [2] Treatment depends on where the cancer is, how large it is, how fast it is growing, and what you prefer. [2]
Small, superficial cancers with low risk of spreading
Curettage and electrodesiccation: scraping off the top of the cancer with a curet, then searing the base with an electric needle. [2]
Laser therapy: an intense beam of light destroys growths, usually with little damage to nearby tissue. [2]
Freezing (cryosurgery): liquid nitrogen freezes cancer cells, sometimes after curetting the surface. [2]
Photodynamic therapy: a light-sensitizing medicine is applied to the skin, then a light destroys the cancer cells. [2]
Larger or deeper cancers
Simple or wide excision: cutting out the cancer and a margin of healthy skin around it. [2]
Mohs surgery: removing the cancer layer by layer and examining each layer under a microscope until no cancer cells remain, which spares as much healthy skin as possible. [2]
Radiation therapy: powerful energy beams kill cancer cells. It is sometimes used after surgery when the cancer might return, or for people who can't or don't want to have surgery. [2]
Cancer that has spread past the skin
Chemotherapy: strong medicines kill cancer cells and may be used alone or with targeted therapy and radiation. [2]
Targeted therapy: medicines attack specific chemicals in cancer cells and are usually used with chemotherapy. [2]
Immunotherapy: medicine that helps the immune system find and kill cancer cells. It may be considered when the cancer is advanced and other treatments aren't an option. [2]
Treatment | How it works | Typical use |
|---|---|---|
Curettage and electrodesiccation | Scrape the top, then sear the base | Small, superficial, low-risk cancers |
Laser therapy | Light beam destroys growths | Small cancers; little damage to nearby tissue |
Cryosurgery | Liquid nitrogen freezes cancer cells | Small cancers |
Photodynamic therapy | Light-sensitive medicine plus light | Small cancers; may be combined with other treatments |
Simple or wide excision | Cut out the cancer with a margin | Larger or deeper cancers |
Mohs surgery | Layer-by-layer removal with microscope checks | Precise removal sparing healthy skin |
Radiation therapy | Powerful energy beams | After surgery if return risk is high, or when surgery isn't possible or wanted |
Chemotherapy, targeted therapy, immunotherapy | Medicines that kill or target cancer cells or boost the immune response | Cancer that has spread or is advanced |
How Should You Prepare for the Appointment?
If a skin sore concerns you, make an appointment with a doctor or other healthcare professional. You may be referred to a dermatologist, a doctor who specializes in skin conditions. [2] If you have already had skin cancer, your risk of another is higher, so ask your dermatologist how often you should have a skin exam. [2]
Ask a family member or friend to come with you to help you remember what you are told. [2]
Make a list of your medical history, including other conditions you've been treated for. [2]
List all your medicines, vitamins, and natural remedies, with doses. [2]
Prepare questions, such as: Do I have skin cancer? What kind? Is it likely to spread, and has it? What treatment do you recommend, and what are the side effects? Will I have a scar? Is it likely to come back? How often will I need follow-up? [2]
Be ready to answer questions about how long you've had the growth, whether it has grown, whether it causes discomfort, any other concerning sores, previous skin cancer, sun exposure in childhood and now, tanning bed use, immune-suppressing medicines, and whether you smoke or smoked. [2]
Conclusion
Squamous cell carcinoma is one of the most common skin cancers and one of the most treatable. It begins in the squamous cells of the skin, appears most often on sun-exposed areas, and is usually not life-threatening when caught early. Because UV radiation causes most cases, prevention is unusually effective: daily sunscreen, midday shade, protective clothing, and avoiding tanning beds all lower your risk.
What are the next steps for squamous cell carcinoma of the skin?
Check your skin regularly, including areas rarely exposed to sun, and book an appointment if any sore, bump, or scaly patch lasts longer than about two months. If you've already had skin cancer, ask your dermatologist how often to have a skin exam. If you've been diagnosed, bring your medical history, medication list, and questions to your appointment, and ask whether Mohs surgery or another option best fits your situation.
Trusted resources: Squamous cell carcinoma of the skin: Symptoms and causes, Squamous cell carcinoma of the skin: Diagnosis and treatment, American Cancer Society: Squamous Cell Skin Cancer
Frequently Asked Questions
What is squamous cell carcinoma of the skin?
It is a common type of skin cancer that starts as a growth of cells on the skin, beginning in squamous cells, which make up the middle and outer layers of the skin.
Is squamous cell carcinoma dangerous?
It is usually not life-threatening when treated. Untreated, it can grow large, spread to other parts of the body, and cause serious complications, and it can rarely be fatal.
Where does squamous cell carcinoma usually appear?
Most often on sun-exposed skin such as the scalp, backs of the hands, ears, and lips, but it can occur anywhere, including inside the mouth, on the bottoms of the feet, or on the genitals.
What does squamous cell carcinoma look like?
A firm bump that may be skin-colored, pink, red, black, or brown; a flat sore with a scaly crust; a new sore on an old scar; a rough scaly patch on the lip; a sore inside the mouth; or a raised wartlike patch on or in the anus or genitals.
When should I see a doctor about a skin sore?
See a healthcare professional for a sore or scab that doesn't heal in about two months, or a flat patch of scaly skin that won't go away.
Does squamous cell carcinoma affect people with darker skin?
Yes, anyone of any skin color can get it. In people with Black and brown skin it is more likely to appear on skin not exposed to sun, such as the genitals.
What causes squamous cell carcinoma?
DNA changes in squamous cells make them multiply quickly and survive longer than normal. UV radiation from sunlight, tanning lamps, and tanning beds causes most of these changes.
What raises the risk?
Skin that sunburns easily, too much sun, tanning beds, blistering sunburns, precancerous lesions such as actinic keratosis, previous skin cancer, a weakened immune system, xeroderma pigmentosum, HPV infection, and scars or long-lasting wounds.
Can squamous cell carcinoma spread?
Yes. Untreated, it can destroy nearby tissue and spread to lymph nodes or organs. The risk is higher if it grows large or deep, involves mucous membranes such as the lips, or occurs in someone with a weakened immune system.
How is it diagnosed?
With a physical exam and health history, followed by a biopsy, in which some or all of the unusual skin area is removed and examined in a laboratory.
How is squamous cell carcinoma treated?
Most cases are removed with minor surgery or a medicine applied to the skin. Small cancers can be treated with curettage and electrodesiccation, laser, freezing, or photodynamic therapy; larger ones may need excision, Mohs surgery, or radiation; and spread may call for chemotherapy, targeted therapy, or immunotherapy.
What is Mohs surgery?
A procedure in which the cancer is removed layer by layer, with each layer examined under a microscope until no cancer cells remain, so the whole growth is removed without taking too much healthy skin.
Is squamous cell carcinoma curable?
Most squamous cell carcinomas of the skin can be removed with minor surgery. Treatment choice depends on location, size, growth rate, and your preferences.
Can it be prevented?
Most can. Avoid midday sun, use broad-spectrum SPF 30+ sunscreen year-round and reapply every two hours, wear protective clothing and a wide-brimmed hat, never use tanning beds, and check your skin regularly.
What should I ask at my appointment?
Ask whether you have skin cancer and what kind, whether it is likely to spread or has spread, which treatment is recommended and its side effects, whether you'll have a scar, whether it could come back, your risk of other skin cancers, and how often you'll need follow-up.
Related Reading
Photodynamic Therapy (PDT): Uses, Procedure, Recovery and Risks explains how a light-activated drug treats precancer and some skin cancers, with recovery and light-safety tips.
Learn more in our guide to Skin Biopsy: Types, What to Expect, Results and Aftercare.
References
Mayo Clinic Staff. Squamous cell carcinoma of the skin: Symptoms and causes. Mayo Clinic. July 26, 2025. https://www.mayoclinic.org/diseases-conditions/squamous-cell-carcinoma/symptoms-causes/syc-20352480
Mayo Clinic Staff. Squamous cell carcinoma of the skin: Diagnosis and treatment. Mayo Clinic. July 26, 2025. https://www.mayoclinic.org/diseases-conditions/squamous-cell-carcinoma/diagnosis-treatment/drc-20352486
Green A, Williams G, Neale R, et al. Daily sunscreen application and betacarotene supplementation in prevention of basal-cell and squamous-cell carcinomas of the skin: a randomised controlled trial. Lancet. 1999;354(9180):723-729. PMID 10475183. https://doi.org/10.1016/S0140-6736(98)12168-2
Salehi AM, Rezaei R, Sadeghi A, et al. Azathioprine increases the risk of non-melanoma skin cancer among organ transplant recipients: an updated systematic review and meta-analysis. Cancer Rep (Hoboken). 2026;9(2):e70473. PMID 41667291. https://doi.org/10.1002/cnr2.70473
Medical Disclaimer
This article is for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional for diagnosis and treatment decisions.
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