What Is Skin Cancer?

A clear, medically reviewed definition and overview adapted from the U.S. National Cancer Institute (NCI) and other trusted sources.

Overview & Definition

Skin cancer is the uncontrolled growth of abnormal cells originating in the skin. Most cases develop on sun-exposed areas, but they can appear anywhere (including scalp, lips, ears, palms/soles, under nails). While many skin cancers grow slowly and are highly curable when detected early, some—especially melanoma—can spread (metastasize) and be life-threatening.

Major Types

Basal cell carcinoma (BCC): the most common; often appears as a pearly or pink bump, or a non-healing sore. Rarely spreads but can invade locally if untreated.
Squamous cell carcinoma (SCC): a scaly, crusted, or wart-like lesion that can grow and sometimes spread; risk increases with chronic sun damage.
Melanoma: arises from pigment-producing melanocytes. Less common but more dangerous because it can spread early. Early detection is critical.
Other rare types: Merkel cell carcinoma, cutaneous lymphomas, and others—managed in specialized settings.

Risk Factors

Ultraviolet (UV) exposure: sunlight and indoor tanning devices; history of sunburns.
Fair skin / light eyes / red or blond hair and skin that burns or freckles easily.
Multiple or atypical moles (dysplastic nevi) and large/giant congenital nevi.
Family or personal history of skin cancer; certain inherited syndromes.
Weakened immune system (e.g., after organ transplant).
Older age (risk increases over time), though melanoma also occurs in younger adults.
Environmental exposures (e.g., arsenic) and prior radiation to the skin.

Anyone can develop skin cancer—regardless of skin tone. Protection and routine checks help catch problems early.

Signs & Symptoms

Watch for new, changing, or unusual spots, sores that don’t heal, or anything that looks different from others (“ugly duckling”). For melanoma, remember the ABCDEs:

A – Asymmetry: one half unlike the other.
B – Border: irregular, scalloped, or poorly defined edges.
C – Color: varied shades of tan, brown, black, sometimes white, red, or blue.
D – Diameter: usually > 6 mm (pencil eraser), but can be smaller.
E – Evolving: looks different from the rest or is changing in size, shape, or color; new symptom like bleeding or itching.

Prevention & Sun Safety

Seek shade (especially 10 a.m.–4 p.m.).
Use broad-spectrum sunscreen SPF 30+; apply generously and reapply every 2 hours and after swimming/sweating.
Wear protective clothing: long sleeves, pants, wide-brim hat, UV-blocking sunglasses.
Avoid tanning beds and intentional tanning.
Self-check monthly and get routine skin exams as advised by your clinician.

See sources

Diagnosis & Staging

Clinicians examine the skin and perform a biopsy (shave, punch, or excisional) of suspicious lesions. Pathology confirms the cancer type and key features (e.g., margins, ulceration, perineural invasion).

Non-melanoma (BCC/SCC): staged mainly by size, depth, high-risk features, and spread to nodes or beyond.
Melanoma: staging uses Breslow depth (tumor thickness), ulceration, lymph node status, and metastasis. A sentinel lymph node biopsy may be recommended for certain depths.

Treatment Options

Surgery is the mainstay for most skin cancers: excisional surgery with margins; Mohs micrographic surgery for selected BCC/SCC (e.g., face, high-risk sites).
Topical/field therapies (for some superficial lesions): 5-FU, imiquimod, photodynamic therapy, cryotherapy.
Radiation therapy for patients who cannot have surgery or as adjuvant treatment in specific cases.
Systemic therapies:
- Melanoma: immune checkpoint inhibitors (PD-1/CTLA-4), targeted therapy for BRAF-mutant disease (BRAF/MEK inhibitors), and others.
- Advanced BCC: hedgehog pathway inhibitors; PD-1 inhibitors in some settings.
- Advanced cSCC: PD-1 inhibitors for unresectable/metastatic disease.
Supportive care (wound care, scar management, lymphedema therapy when nodes treated).

Prognosis

Most BCCs and SCCs are curable with appropriate treatment. Melanoma prognosis depends strongly on tumor thickness and spread—early detection dramatically improves outcomes. Regular skin checks and sun protection are key.

Sources & Attribution

Adapted primarily from the U.S. National Cancer Institute (NCI) and supported by CDC and MedlinePlus:

NCI — Skin Cancer (Non-melanoma): cancer.gov/types/skin
NCI — Melanoma: cancer.gov/types/skin/melanoma
CDC — Skin Cancer Prevention: cdc.gov/cancer/skin
MedlinePlus — Skin Cancer: medlineplus.gov/skincancer.html

This content is educational and not a substitute for professional medical advice. If you notice a changing spot or non-healing sore, see a qualified clinician.

Skin Cancer