Skin cancer

The three kinds, and how they show up

• Basal cell carcinoma. The most common by far. A pearly bump that bleeds easily, scabs over and opens again. Grows slowly and almost never spreads — but it destroys what is around it.
• Squamous cell carcinoma. A rough, scaly or ulcerated patch, often on the lip, the ear or the back of the hand. Frequently grows out of a solar keratosis.
• Melanoma. The least frequent and the most serious. Usually a mole that changed.

The one sign worth memorizing

A sore that has not healed in a month is not a pimple. It is the single most useful rule in this whole page, and it is the one people ignore because the thing doesn't hurt.

Also worth a visit without waiting: a lesion that bleeds on its own, one that grows steadily, and any mole that changed.

How it is diagnosed

A full-skin examination with a dermatoscope, which shows the structure underneath the surface instead of only the color on top. When follow-up is needed, digital mole mapping photographs each lesion so next year's exam is a comparison rather than a memory.

If there is any doubt, a biopsy under local anesthesia. The diagnosis comes from the pathology report, not from the eye — which is also why nothing can be ruled out from a photograph.

Who should be checked every year

• Fair skin that burns rather than tans.
• Bad sunburns in childhood.
• Years of outdoor work or outdoor sport.
• Many moles, or large moles present since birth.
• A personal or family history of skin cancer.

Anyone who has already had one skin cancer is more likely to have another: the skin in that area carries accumulated damage. That is why follow-up matters.