Skin cancer is the most common cancer and most cases are linked to ultraviolet light from the sun or tanning beds. Each type starts in a different cell of the epidermis.
How it starts
Ultraviolet light damages the DNA of skin cells. Over years, the damage can let cells grow out of control, which is why risk rises with age, sunburns and fair skin.
Basal cell carcinoma
The most common type, from the base of the epidermis. It looks like a pearly or shiny bump, often with small vessels, grows slowly and rarely spreads.
Squamous cell carcinoma
Starts in keratinocytes, often on sun-exposed skin, as a scaly, crusted or sore bump. It can spread to lymph nodes if left untreated.
Melanoma
Starts in melanocytes, the pigment cells, and can appear as a new or changing mole. It is less common but spreads early, so it causes most skin cancer deaths.
| Type | Starts in | Typical look |
|---|---|---|
| Basal cell carcinoma | Basal cells | Pearly bump, small vessels |
| Squamous cell carcinoma | Keratinocytes | Scaly, crusted or ulcerated bump |
| Melanoma | Melanocytes | Irregular, dark or changing mole |
At the bedside
Check moles with the ABCDE rule: asymmetry, irregular border, uneven color, diameter over 6 mm and evolving. Any changing, bleeding or new unusual spot should be referred for a closer look.
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Written by Making Synapses. Topic reference: OpenStax, Anatomy and Physiology 2e (no text adapted).