In short. Most pigmented spots are harmless, but some are not; how a dermatologist decides what to examine, monitor, or remove.
Key points
- This is the single rule that prevents the worst outcomes in pigment practice.
- Laser treatment, cryotherapy, and lightening creams all remove pigment, and with it the evidence a pathologist needs.
- If a lesion turns out to be a skin cancer, the treatment has delayed the diagnosis and may have made complete removal more difficult.
Most pigmented spots are harmless, and most people who ask about one can be reassured. The reason dermatologists still examine every one of them carefully is that the harmless majority and the dangerous minority look alike, and the difference cannot be judged from a photograph or from how long a spot has been there.
Diagnosis begins with the naked eye and continues with dermoscopy, a magnified, polarised view that reveals structures within a lesion invisible to ordinary inspection. Those structures — pigment networks, dots, globules, streaks, and the way vessels are arranged — are what allow an experienced examiner to distinguish a lentigo from a seborrhoeic keratosis, and both from a melanoma, without cutting anything.
What raises suspicion
The familiar list is asymmetry, an irregular or notched border, several colours within one lesion, a diameter that is large, and any change over time. A sixth criterion is often more useful than all of them: the lesion that looks different from its neighbours — the so-called ugly duckling sign. Also worth examining are a new pigmented lesion appearing in adulthood, a spot that bleeds, itches, or crusts, a sore that will not heal, and any pigmented lesion on a site that has had heavy cumulative sun exposure, where a flat brown patch can be lentigo maligna, a melanoma in situ that grows slowly over years and is easily mistaken for a sun spot.
Never treat what has not been diagnosed
This is the single rule that prevents the worst outcomes in pigment practice. Laser treatment, cryotherapy, and lightening creams all remove pigment, and with it the evidence a pathologist needs. If a lesion turns out to be a skin cancer, the treatment has delayed the diagnosis and may have made complete removal more difficult. Where there is any doubt, the correct step is examination, and then a sample.
How a sample is taken
For a lesion that needs to be excluded as melanoma, the preferred method is complete excision with a narrow margin, because it allows the pathologist to assess the whole lesion and, if necessary, to measure its depth — the single most important prognostic measurement. For large lesions on cosmetically sensitive sites, or where the diagnosis is unclear but not urgently suspicious, an incisional or punch sample from the most representative area may be taken instead. What is avoided for suspected melanoma is a superficial shave or a destructive procedure, both of which can leave the deepest part of the lesion unexamined.
The result does not always end the process. A borderline or uncertain report may lead to further excision, to a second opinion on the slides, or to close follow-up. That is normal practice, not a sign that something went wrong.
Arrange an assessment without delay if
- A pigmented lesion is changing in size, shape, or colour, or looks different from the others around it.
- A lesion bleeds, itches, crusts, or a sore in the same place fails to heal.
- You are offered laser, freezing, or a cream for a pigmented lesion that has not first been examined and diagnosed.
Frequently asked questions
How does a dermatologist decide whether a spot needs a biopsy?
Dermoscopy reveals structures within a lesion invisible to ordinary inspection, such as pigment networks, dots, globules and vessel arrangement. Asymmetry, an irregular border, several colours, a large diameter and any change raise suspicion, as does the lesion that simply looks different from its neighbours.
Why should a pigmented lesion never be treated before it is diagnosed?
Laser treatment, cryotherapy and lightening creams all remove pigment, and with it the evidence a pathologist needs. If the lesion turns out to be a skin cancer, the treatment has delayed the diagnosis and may have made complete removal more difficult. Examination and a sample come first.
How is a suspicious pigmented lesion sampled?
For a lesion that needs to be excluded as melanoma, the preferred method is complete excision with a narrow margin, which lets the pathologist assess the whole lesion and measure its depth. Large lesions on sensitive sites may be sampled instead. A superficial shave is avoided.
Risks & Limitations
- Most chronic skin disease is managed rather than cured, and relapse is expected.
- Treatments typically need 8–12 weeks before response can be judged fairly.
- Topical treatment can cause irritation, dryness, peeling and photosensitivity.
- Systemic therapy may require blood monitoring and carries organ, metabolic and pregnancy risks.
- Isotretinoin in particular requires strict monitoring and pregnancy prevention.
- Pigment change is often slow and may be incomplete.
- No treatment works for everyone, and response cannot be predicted with certainty.
When to Seek Care
- A mole or lesion that changes in size, shape or colour, or starts to bleed, itch or crust.
- Fever with a widespread rash, blistering, or rash involving the eyes, mouth or genitals — seek emergency care.
- Rapidly spreading redness, swelling or pain in the skin.
- Facial swelling or difficulty breathing — possible severe reaction; seek emergency care immediately.
- New or worsening symptoms while taking a monitored medication.
References & Further Reading
- American Academy of Dermatology (AAD) — public and clinical guidance
- World Health Organization (WHO) — skin and infectious disease resources
- Chinese Medical Association, Dermatology Branch — clinical guidance
- Cochrane Library — systematic reviews in dermatology
This page is patient education, not medical advice, and it does not cite individual studies. Discuss your own case with a qualified clinician. To arrange an assessment at Chongqing West District Hospital, see Contact & Consultation.