Skin cancer develops when abnormal cells in the skin grow out of control, most often triggered by damage from ultraviolet rays. This common form of cancer affects millions of people worldwide, but when caught early, most cases can be successfully treated with minimal complications.

Understanding Skin Cancer

Skin cancer begins in the epidermis, which is the outermost layer of skin that protects your body from the environment. This layer contains different types of cells, each capable of developing into cancer. The three most common types of skin cancer are basal cell carcinoma, squamous cell carcinoma, and melanoma.^[1]

Basal cell carcinoma starts from the basal cells found in the deepest part of the epidermis. Squamous cell carcinoma develops from squamous cells, which are the flat cells forming the upper layers of the epidermis. These two types together are often called non-melanoma skin cancers because they behave differently than melanoma and generally grow more slowly.^[2]

Melanoma develops from melanocytes, which are cells that produce melanin, the pigment that gives skin its color. Although melanoma is less common than basal or squamous cell cancers, it is more dangerous because it can spread to other parts of the body more easily. This spreading ability makes melanoma responsible for most skin cancer deaths, despite its lower frequency.^[3]

The skin also contains other specialized cells that can occasionally develop into rarer forms of cancer. These include Merkel cell carcinoma, which is an aggressive type that forms from cells near nerve endings in the skin. Other uncommon types include Kaposi sarcoma and various skin lymphomas.^[4]

How Common Is Skin Cancer?

Skin cancer stands as the most common cancer diagnosed in the United States. About one in five people will develop skin cancer at some point during their lifetime. This makes it more prevalent than all other cancer types combined when looking at annual new cases.^[4]

The actual number of non-melanoma skin cancers cannot be counted precisely because reporting to cancer registries is not required for these cancers. However, based on extrapolation from available data, researchers estimated that approximately 3.3 million people were treated for non-melanoma skin cancers in 2012 alone. This number exceeds the total of all other new cancer cases combined, which typically number around 2 million annually.^[15]

Despite being the most frequently diagnosed cancer, skin cancer accounts for less than 0.1% of deaths caused by cancer overall. This low death rate reflects the fact that most skin cancers can be successfully treated, especially when detected early. The incidence of non-melanoma skin cancer appears to be increasing in various areas, though experts believe at least some of this increase may result from greater awareness leading people to seek examination and treatment for suspicious skin changes.^[15]

What Causes Skin Cancer to Develop?

The primary cause of skin cancer is overexposure to ultraviolet (UV) radiation, particularly from sunlight. UV rays damage the DNA inside skin cells, causing mutations that lead cells to multiply rapidly and form abnormal masses. When skin is exposed to the sun, this damage accumulates over years, from prolonged outdoor exposure to simple everyday activities like walking to your car or checking your mail.^[2]

Artificial sources of UV radiation, such as tanning beds and sunlamps, also cause skin cancer. These devices emit concentrated UV rays that can damage skin cells just as sunlight does. The damage from UV radiation is particularly dangerous because it is both cumulative and often invisible—you don’t always see or feel the harm being done until cancer develops years later.^[10]

UV radiation is especially sneaky in how it reaches your skin. It penetrates through clouds, meaning you can experience sun damage even on overcast days. UV rays also reflect off surfaces like water, sand, snow, and concrete, exposing your skin from multiple angles. They can even pass through glass, though to a lesser degree, which means you can get some UV exposure while driving or sitting near windows.^[18]

Who Is Most at Risk?

Anyone can develop skin cancer regardless of their race, gender, or age. However, certain characteristics and behaviors significantly increase a person’s risk. People with fair complexions face higher risk because their skin contains less melanin, the protective pigment that helps shield skin from UV damage. This includes individuals with fair skin that freckles and burns easily, light-colored eyes like blue or green, and red or blond hair.^[10]

A history of sunburns, particularly blistering sunburns during childhood or adolescence, substantially raises skin cancer risk. Each sunburn represents an episode of severe DNA damage to skin cells, increasing the likelihood of mutations that can lead to cancer. People who have experienced frequent sunburns throughout their lives carry this elevated risk forward.^[15]

Having many moles or unusual moles increases melanoma risk specifically. People with more than 50 moles, or those with atypical moles that have irregular borders, multiple colors, or change over time, should be especially vigilant. A family history of melanoma or unusual moles also elevates risk, suggesting genetic factors play a role in susceptibility.^[10]

Personal medical history matters as well. Anyone who has previously had skin cancer faces increased risk of developing another skin cancer. Individuals who underwent radiation therapy or were exposed to toxic materials like arsenic also have higher risk. Certain viral infections, particularly some subtypes of human papillomavirus, have been linked to squamous cell carcinoma development.^[15]

People with weakened immune systems face greater skin cancer risk. This includes organ transplant patients taking immunosuppressant medications, which prevent their bodies from rejecting transplanted organs but also reduce their ability to fight cancer cell formation. Similarly, individuals with chronic non-healing wounds or burn injuries have elevated risk in those affected areas.^[15]

Although people with darker skin have more natural protection from melanin, they can and do develop skin cancer. Melanoma in people of color often appears in unexpected locations such as the palms of the hands, soles of the feet, or under the nails—areas that typically receive less sun exposure. This highlights that skin cancer isn’t exclusively a disease of sun-damaged skin.^[10]

Recognizing the Symptoms

The most common warning sign of skin cancer is a change on your skin. This might appear as a completely new growth, a new mole, or changes in an existing mole or other skin feature. Any alteration in size, shape, color, or texture of a skin growth deserves attention and should prompt a conversation with your doctor.^[3]

Basal cell carcinoma often presents as a pearly or waxy bump, typically appearing on the face, ears, or neck—areas that receive frequent sun exposure. It might also look like a flat, pink, red, or brown-colored patch or bump. Sometimes these growths resemble scars, appearing as areas that look slightly different from surrounding skin.^[4]

Squamous cell carcinoma commonly appears as a rough, scaly patch or lesion. These areas might itch, bleed, and develop a crusty surface. They can also present as sores that look crusty or have a depression in the middle. A key warning sign is a wound or sore that won’t heal properly, or one that seems to heal but then returns.^[11]

For melanoma, doctors recommend thinking about the ABCDE rule when examining moles or other skin marks. A stands for Asymmetry—one half of the mole doesn’t match the other half. B represents Border irregularity, with blurry or jagged edges. C indicates Color variation, meaning the mole contains more than one color or has uneven color distribution. D refers to Diameter, particularly moles larger than a pencil eraser (about 6 millimeters). E stands for Evolution, which is the most important sign—any mole that is changing in size, shape, or color requires immediate medical attention.^[11]

Skin cancer can develop anywhere on the body, though it most commonly appears on areas frequently exposed to sunlight such as the face, neck, hands, and arms. However, cancers can also develop in areas that rarely see sun, including between toes, on the palms of hands, soles of feet, and under fingernails or toenails.^[10]

Prevention Strategies That Work

Preventing skin cancer requires a comprehensive approach to protecting yourself from UV radiation. Since most skin cancers result from sun exposure, limiting UV contact significantly reduces your risk. The most effective strategy combines multiple protective measures used consistently throughout life.^[18]

Seeking shade represents one of the simplest protective actions, especially during peak sun hours between 10 a.m. and 4 p.m. when the sun’s rays are strongest. Planning outdoor activities for early morning or late afternoon naturally reduces UV exposure. When outdoors during midday, staying under trees, umbrellas, or other shade sources provides meaningful protection.^[21]

Covering your skin with protective clothing creates a physical barrier against UV rays. Long-sleeved shirts, long pants or skirts, and broad-brimmed hats that shade your face, ears, and neck offer excellent protection. Clothing made from tightly woven fabrics in darker colors generally provides better UV blocking. Some clothing manufacturers now produce garments specifically designed with UV protection, which can be particularly useful for people spending extended time outdoors.^[18]

Sunscreen remains an essential tool when skin must be exposed. Choose a broad-spectrum product with SPF 30 or higher that protects against both UVA and UVB rays. Look for ingredients like titanium dioxide or avobenzone on the label. Apply sunscreen generously—most people don’t use enough—about one ounce (two tablespoons) to cover the entire body. Application should happen 30 minutes before going outside, with reapplication every two hours, or more frequently after swimming or heavy sweating.^[18]

Don’t forget often-overlooked areas like the lips, ears, back of the neck, tops of feet, and parts in your hair. Lips need protection through lip balm with SPF 15 or higher. Sunglasses that block 100% of UV rays protect both your eyes and the delicate skin around them from damage.^[20]

Avoiding indoor tanning represents another crucial preventive measure. Tanning beds, booths, and sunlamps emit concentrated UV radiation that damages skin just as sunlight does. There is no such thing as a safe tan from these devices. People who use tanning beds before age 35 significantly increase their melanoma risk.^[21]

Protecting children from excessive sun exposure and sunburns is particularly important. Keeping newborns completely out of the sun provides the best protection for their sensitive skin. For babies over six months, sunscreen can be used along with protective clothing and shade. Since most sun exposure occurs before age 18 and skin damage is cumulative, establishing good sun protection habits early provides lifelong benefits.^[20]

Regular self-examination of your skin helps detect changes early. Checking your entire body monthly, including hard-to-see areas with mirrors or a partner’s help, allows you to become familiar with your normal skin appearance. Any new growths, changing moles, or persistent sores should prompt a visit to your doctor.^[18]

Annual professional skin examinations by a dermatologist provide expert screening. Dermatologists are trained to identify suspicious lesions that might escape a person’s notice. These yearly checks are especially important for people with risk factors like fair skin, many moles, or previous skin cancers.^[18]

How the Body Changes With Skin Cancer

Normally, skin cells follow an orderly process of growth, maturation, and death. New cells form in the deeper layers of the epidermis and gradually move toward the surface as they mature. When they reach the top layer, they die and shed off, making room for newer cells beneath. This continuous cycle keeps your skin healthy and functioning properly.^[11]

Skin cancer disrupts this normal process when UV radiation damages the DNA within skin cells. This damage causes mutations—errors in the genetic instructions that control how cells grow and divide. When these mutations affect certain critical genes, cells lose their normal controls and begin multiplying too rapidly.^[11]

Instead of maturing properly and eventually dying, the abnormal cells continue dividing in a disorganized way. They form a mass of cancer cells that grows into a tumor. In basal cell and squamous cell carcinomas, these tumors typically remain localized, growing slowly in the area where they originated. They can invade deeper into surrounding tissue, damaging healthy structures nearby, but they rarely spread to distant body parts.^[10]

Melanoma behaves more aggressively because melanocytes naturally have the ability to move through tissues. When melanocytes become cancerous, they retain this mobility. Melanoma cells can break away from the original tumor and travel through the bloodstream or lymphatic system to other organs. Once melanoma spreads, it can form new tumors in the liver, lungs, brain, bones, or other locations. This spreading process, called metastasis, makes melanoma much more dangerous and harder to treat.^[3]

The skin’s protective functions can become compromised when cancer develops. Affected areas may lose their normal ability to act as a barrier against infection and injury. As tumors grow, they can damage blood vessels and nerves in the skin, leading to bleeding, pain, or changes in sensation. Large or deeply invasive skin cancers may affect the appearance and function of the affected body part.^[1]

The immune system normally works to identify and destroy abnormal cells, including cancer cells. However, cancer cells often develop ways to evade immune detection or suppress immune responses. This allows them to continue growing despite the body’s natural defenses. Some newer treatments for skin cancer work by helping the immune system recognize and attack cancer cells more effectively.^[7]