How UV damages skin

Ultraviolet radiation damages DNA in skin cells. Most damage is repaired, but errors accumulate over a lifetime and can lead to skin cancer. Two wavelengths matter for everyday exposure.

  • UVB — mainly causes sunburn and directly damages DNA. Strongest in the middle of the day and in summer.
  • UVA — penetrates deeper, drives most photoageing, and contributes to cancer risk. Present throughout daylight hours and passes through window glass.

Sunburn, particularly blistering burns in childhood, is associated with higher melanoma risk. But damage accumulates without burning too, which is why daily incidental exposure matters for people who spend time outdoors.

A tan is itself a sign of DNA damage — the skin producing melanin in response to injury. There is no such thing as a safe tan from UV exposure.

Choosing and using sunscreen properly

Application technique matters more than most people realise. SPF ratings are established using a thicker layer than almost anyone applies, so real-world protection is typically well below the number on the bottle.

  • Choose broad-spectrum, SPF 30 or higher; water-resistant if swimming or sweating.
  • Apply generously — roughly a shot glass full for the whole body, and about a teaspoon for face and neck.
  • Apply 15 minutes before going out.
  • Reapply every two hours, and immediately after swimming, towelling, or heavy sweating.
  • Do not forget ears, back of the neck, tops of feet, hands, scalp partings, and lips with an SPF balm.

Mineral filters such as zinc oxide and titanium dioxide, and chemical filters, both work. Choose what you will actually reapply. Sunscreen is one layer of protection, not a licence for longer exposure.

Beyond sunscreen

Sunscreen is the layer people think of first, but it is the least reliable in practice because it depends on correct application. The other measures are more forgiving.

  • Shade during peak UV, roughly 10am to 4pm.
  • Clothing — tightly woven fabric, long sleeves, or rated UPF clothing. It does not wear off.
  • A wide-brimmed hat — better than a cap, which leaves ears and neck exposed.
  • Sunglasses with UV protection; UV contributes to cataracts and eyelid cancers.
  • Check the UV index — protection is generally advised at 3 or above.

Remember that UV reflects off water, sand, concrete, and snow, and increases with altitude. Cloud cover does not block it reliably. Tanning beds should be avoided entirely; they are classified as carcinogenic to humans.

Checking your skin

Knowing what is normal for your own skin is the practical goal. Check yourself periodically, using a mirror or asking someone for your back and scalp.

The ABCDE features describe changes worth getting checked:

  • A — Asymmetry: one half unlike the other.
  • B — Border: irregular, scalloped, or poorly defined.
  • C — Colour: varied shades, or new colours within one lesion.
  • D — Diameter: larger than about 6 mm, though melanomas can be smaller.
  • E — Evolving: changing in size, shape, colour, or symptoms. This is the single most important feature.

The ugly duckling sign is also useful: a lesion that simply looks different from your other moles. Also report any sore that does not heal within a few weeks, a scaly or crusted patch that persists, or a new lump that grows.

Skin tone, vitamin D, and common misconceptions

Higher melanin provides some natural protection, but skin cancer occurs in people of every skin tone. In darker skin it is more often diagnosed at a later stage and more frequently occurs in less sun-exposed areas — palms, soles, under nails, and in the mouth. Those areas deserve attention during a self-check.

On vitamin D: sun exposure is a source, and this is sometimes used to argue against sun protection. Most people can maintain adequate levels through diet, fortified foods, and supplementation when needed, without deliberate UV exposure. If you are concerned about vitamin D, ask about testing rather than sunbathing.

  • Sunscreen used in real-world amounts does not typically cause vitamin D deficiency.
  • Base tans do not provide meaningful protection.
  • Some medications increase photosensitivity — ask a pharmacist.
  • See a clinician promptly about any changing lesion rather than watching it for months.