How skin cancer develops

Skin cancer forms when cells in the skin grow abnormally. Most often, this happens because DNA inside skin cells gets damaged—usually by ultraviolet (UV) radiation from the sun or from tanning beds. When that damage occurs, the cell's instructions for normal growth break down. Instead of dividing at a controlled rate and then dying on schedule, the damaged cell divides repeatedly and can spread to other parts of the body.

The damage doesn't always cause cancer immediately. It can take years or even decades for enough mutations to pile up inside a cell before it becomes cancerous. This is why skin cancer is more common as people age, and why sun exposure in childhood matters even if cancer doesn't appear until adulthood.

Not everyone exposed to UV radiation develops skin cancer. Genetics, skin tone, immune system strength, and the total amount of sun exposure all play a role in whether damaged cells will eventually turn into cancer.

Key Takeaways

  • UV radiation from the sun or tanning beds damages DNA in skin cells, and repeated damage over years can lead to cancer.
  • Fair skin, a family history of skin cancer, and a weakened immune system all increase the risk that UV damage will become cancer.
  • Most skin cancers are basal cell or squamous cell carcinoma, which grow slowly and rarely spread; melanoma is rarer but more dangerous.
  • Sunburns, especially severe ones in childhood, signal that DNA damage has occurred, even if cancer doesn't develop for decades.
  • Reducing UV exposure through sunscreen, shade, and protective clothing lowers the chance that existing damage will progress to cancer.

Ultraviolet radiation and DNA damage

UV radiation is energy from the sun that reaches Earth in two main forms: UVA and UVB. Both can damage the DNA inside skin cells. UVB rays are stronger and cause sunburns more directly. UVA rays penetrate deeper into the skin and cause damage that may not show up as a burn but still alters cell DNA over time.

When UV rays hit a skin cell, they can break the bonds that hold DNA together. The cell has repair systems that usually fix this damage, but if the damage is too severe or happens too often, repairs fail. A mutation—a permanent change in the cell's genetic code—takes hold. One mutation alone rarely causes cancer, but when the same cell accumulates multiple mutations over years, it can lose the ability to control its own growth.

Tanning beds emit UVA and UVB radiation in concentrated doses. A single tanning session delivers UV exposure comparable to several hours in the sun, which is why dermatologists consider tanning beds a significant risk factor for skin cancer.

Who is at higher risk

People with fair or light skin have less melanin—the pigment that absorbs UV radiation and protects cells from damage. This means UV rays penetrate more easily and cause more DNA damage per unit of exposure. People with darker skin have more melanin and are at lower risk, though skin cancer still occurs in all skin tones and is often diagnosed later in darker skin because it may be overlooked.

A family history of skin cancer means you inherited genes that make your cells more vulnerable to UV damage or less able to repair it. If a parent or sibling had skin cancer, your risk is higher even with the same sun exposure.

A weakened immune system—from HIV, organ transplant medications, or certain cancers—reduces the body's ability to destroy cells that have become abnormal. People in this situation develop skin cancer at younger ages and sometimes develop multiple cancers.

Age also matters. Skin cancer is more common in older adults because damage accumulates over a lifetime. However, melanoma can appear in young people, and the incidence in people under 40 has been rising for decades.

Types of skin cancer and how they form

Basal cell carcinoma starts in the basal cells at the base of the epidermis (the outermost layer of skin). It accounts for about 80 percent of all skin cancers. It grows slowly, rarely spreads to other parts of the body, and is almost always curable if caught early. It usually appears as a shiny bump, a scar-like patch, or a sore that doesn't heal.

Squamous cell carcinoma begins in the flat cells in the upper part of the epidermis. It accounts for roughly 15 to 20 percent of skin cancers. It also grows slowly and rarely spreads, though it is more likely to spread than basal cell carcinoma. It often looks like a scaly patch, a wart, or a sore with raised edges.

Melanoma starts in melanocytes—the cells that produce melanin. It accounts for only 1 to 2 percent of skin cancers but causes the majority of skin cancer deaths because it spreads more readily. Melanoma can appear as a new mole or as a change in an existing mole. The ABCDE rule helps identify suspicious moles: Asymmetry (one half doesn't match the other), Border irregularity, Color variation, Diameter larger than a pencil eraser, and Evolution (change over time).

Sunburns as a warning sign

A sunburn is visible evidence that UV radiation has damaged skin cells. The redness and pain come from inflammation as the body responds to that damage. Severe sunburns, especially repeated ones or ones that happen in childhood, significantly increase skin cancer risk.

Even a sunburn that fades completely means DNA damage has occurred inside the cells. Some of that damage gets repaired, but some may persist as mutations. Over decades, these mutations can accumulate in the same cell until it becomes cancerous.

People who have had five or more severe sunburns have roughly double the risk of melanoma compared to those who have never had a severe burn. This is one reason why sun protection in childhood is considered so important—the damage done then can lead to cancer 20, 30, or 40 years later.

Other risk factors beyond sun exposure

Certain chemicals and conditions increase skin cancer risk independently of sun exposure. Exposure to arsenic—which can occur through contaminated drinking water in some regions—raises the risk of squamous cell carcinoma. Occupational exposure to coal tar, paraffin, or certain pesticides also increases risk.

People with a condition called xeroderma pigmentosum have defective DNA repair systems. Their cells cannot fix UV damage effectively, so they develop skin cancer at very young ages even with minimal sun exposure. This rare genetic condition demonstrates how critical DNA repair is to preventing cancer.

Scars from burns, injuries, or chronic wounds can occasionally develop into squamous cell carcinoma years later, even without additional sun exposure. The constant inflammation and cell turnover in healing tissue creates an environment where abnormal growth is more likely.

How reducing UV exposure lowers cancer risk

Because UV radiation is the primary cause of most skin cancers, reducing exposure prevents new DNA damage and lowers the chance that existing damage will progress to cancer. Sunscreen with SPF 30 or higher blocks about 97 percent of UVB rays. Broad-spectrum sunscreen also protects against UVA. Reapplying every two hours, or after swimming or sweating, maintains protection.

Seeking shade during peak sun hours (10 a.m. to 4 p.m.) reduces exposure significantly. Protective clothing—long sleeves, pants, hats, and sunglasses—physically blocks rays. UV-blocking fabrics are now common in athletic and outdoor wear.

Avoiding tanning beds eliminates a concentrated source of UV radiation. The American Academy of Dermatology recommends against tanning beds for anyone, and many countries have restricted their use in minors.

These measures cannot erase damage that has already occurred, but they prevent new damage and give the body a better chance to repair existing mutations before they become cancer.

Frequently Asked Questions

Can you get skin cancer without ever being sunburned?

Yes. UV damage accumulates gradually, and many people develop skin cancer from chronic low-level sun exposure over decades without ever having a severe sunburn. Fair-skinned people who tan easily but rarely burn are still at risk. Additionally, people with genetic conditions or weakened immune systems can develop skin cancer with minimal sun exposure.

Does sunscreen prevent all skin cancer?

Sunscreen significantly reduces risk but does not prevent all skin cancer. No sunscreen blocks 100 percent of UV rays. People who rely only on sunscreen without also seeking shade or wearing protective clothing still accumulate UV exposure. Sunscreen works best as part of a complete sun protection strategy.

If I had a lot of sun exposure as a child, am I may provide to get skin cancer?

No. Many people with heavy childhood sun exposure never develop skin cancer, especially if they have darker skin or genes that repair DNA more effectively. However, childhood sun exposure does increase risk, which is why reducing exposure now—even decades later—still matters.

Can skin cancer run in families?

Yes. Families can inherit genes that make skin cells more vulnerable to UV damage or less able to repair it. If multiple family members have had skin cancer, your risk is higher. However, genetics is not destiny—sun protection is still effective even for people with a family history.

Is skin cancer on the face more serious than skin cancer elsewhere?

The location affects treatment options and cosmetic outcome but not the seriousness of the cancer itself. Melanoma on the face, scalp, or ears may be more aggressive than melanoma on the trunk or limbs, but this is a property of the cancer cells, not the location. Basal cell and squamous cell carcinomas are generally serious only if left untreated for a long time.