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When to see a dermatologist: moles, rashes and the ABCDEs

How to check moles with the ABCDE rule and the ugly duckling sign, other reasons to see a dermatologist, and the sun protection habits that lower skin cancer risk.

Updated 6 min read dr.clinic editorial team How we write

Key takeaways

  • Check your skin monthly and look for spots that are changing or look different from the rest.
  • Use the ABCDE rule: asymmetry, border, colour, diameter and evolving.
  • Broad-spectrum SPF 30+ sunscreen, shade and covering up reduce skin cancer risk.

Most moles and skin spots are harmless. But skin cancer is very common, and melanoma — the most serious type — is far more treatable when found early. A monthly self-check takes five minutes.

The ABCDEs of melanoma

  • A — Asymmetry: one half does not match the other.
  • B — Border: ragged, notched or blurred edges.
  • C — Colour: several shades of brown or black, or patches of red, white or blue.
  • D — Diameter: larger than about 6 mm (the size of a pencil eraser), although melanomas can be smaller.
  • E — Evolving: changing in size, shape, colour or height, or new symptoms such as itching, crusting or bleeding.

Also watch for the “ugly duckling” — a spot that looks different from your other moles.

How to check your skin

  1. Use a full-length mirror and a hand mirror in good light.
  2. Check everywhere, including your scalp, palms, soles, between toes, under nails and genital area.
  3. Ask a partner to check your back, or take photos so you can compare over time.

Other reasons to see a dermatologist

  • A sore or spot that does not heal within a few weeks
  • Acne that is not responding to over-the-counter treatment or is leaving scars
  • Eczema or psoriasis that is hard to control
  • Sudden or patchy hair loss, or nail changes
  • Persistent itching, rashes or hives

In some health systems you will need to see primary care first for a referral. Your clinician can arrange an urgent referral for a suspicious spot.

Seek urgent care for a rapidly spreading red, hot or painful area of skin, especially with fever, or a widespread blistering rash. Call your emergency number for a rash with swelling of the face, lips or tongue, or difficulty breathing.

Sun protection that works

  • Use broad-spectrum sunscreen with SPF 30 or higher, applied generously and reapplied every two hours and after swimming or sweating.
  • Seek shade during the middle of the day, and wear a wide-brimmed hat, sunglasses and covering clothes.
  • Avoid tanning beds.

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Sources and further reading

  1. American Academy of Dermatology: What to look for — the ABCDEs of melanoma
  2. MedlinePlus: Skin cancer
  3. NHS: Moles

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