In short. Depth, colour, border, reactivity and history: the questions a clinician works through before choosing a light source for a pigmented lesion, and when to stop.
Key points
- Melasma — symmetrical, hormonal, sun-sensitive pigment across the cheeks, upper lip and forehead — is the clearest case of pigment that light can worsen.
- It is not a discrete target, it is reactive, and treatment can inflame it into a darker and more stubborn state.
- It is managed mainly with sun protection and topical treatment, and any light treatment for it is cautious, at low settings, with the patient warned in advance.
A pigmented lesion is not a diagnosis. Freckles, sun spots, hormonal pigment, a mole, a birthmark, tattoo ink and a scar can all be dark, and each behaves differently under light. Matching a light source to a spot is therefore an assessment rather than a preference, and it comes before any discussion of which machine is used.
The five questions
Depth. How deep the pigment sits decides which wavelengths can reach it and how much energy the skin above absorbs on the way. Pigment in the upper layer responds to a broadband source; pigment sitting deeper may need the energy of a very short pulse, and some depths are not reachable safely at all. Colour. Brown, grey, blue-black and red pigment are different targets, and redness within a lesion suggests vessels rather than melanin. Border. A well-defined edge is a defined target. An edge spread across an area is a broadband problem, and a lesion with an irregular or changing border is a diagnostic problem first. Reactivity. How this person's skin has responded to injury or previous treatment predicts how it will respond to light, and a history of pigment change after a scrape or an earlier session changes the plan. History. When it appeared, and whether it has changed.
Melasma is the exception that proves the rule
Melasma — symmetrical, hormonal, sun-sensitive pigment across the cheeks, upper lip and forehead — is the clearest case of pigment that light can worsen. It is not a discrete target, it is reactive, and treatment can inflame it into a darker and more stubborn state. It is managed mainly with sun protection and topical treatment, and any light treatment for it is cautious, at low settings, with the patient warned in advance. A clinic offering an aggressive course for melasma is offering the treatment most likely to worsen it.
Why the same spot can be treated two ways
Where a lesion is superficial, discrete and stable, a broadband source and a picosecond pulse can both reduce it, and the choice depends on how many there are, how the skin has responded before, and the downtime accepted. Where it is deep, packed or resistant, the shorter pulse reaches it. Where it is diffuse, a broadband source covers it. Where it is hormonal, reactive or unidentified, the right answer may be neither. None of these is a ranking of technology; each is a statement about a target.
Things that should stop a light treatment
- A lesion that has changed in size, shape or colour, or that bleeds, itches or will not heal. It is examined, and often sampled, first.
- Melasma, or pigment that previous light treatment has already made darker. More aggressive treatment is the likely cause of the next worsening.
- Recent sun exposure or a tan. Treating recently exposed skin raises the risk of a pigmentary change, and a course is usually deferred until the skin settles.
Saying no
The useful question is not which light source is stronger but what the spot is made of and where it sits. A clinician who will say that a particular lesion should not be treated with light at all is doing the assessment rather than the sales conversation.
Frequently asked questions
What decides which light source suits a pigmented lesion?
Five things, and all of them come from looking at the skin. How deep the pigment sits decides which wavelengths can reach it. Its colour tells you whether the target is melanin or vessels. Its border tells you whether it is a defined target or an area. How the skin has reacted to injury or previous treatment predicts how it will react to light. And the history — when it appeared and whether it has changed — decides whether it should be treated at all.
Can light treatment make pigmentation worse?
Yes, and melasma is the clearest example. It is symmetrical, sun-sensitive, often hormonal and reactive, and inflammation makes it darker and more stubborn. Light treatment is a controlled form of inflammation, so an aggressive course can leave the skin worse than it started, and the worsening can take months to settle. Melasma is managed mainly with sun protection and topical treatment, and where light is used at all it is used cautiously and at low settings.
Should a mole ever be treated with light?
Not before it has been examined. A lesion that is new, changing in size, shape or colour, bleeding, itching or failing to heal is a diagnostic question first, and treating it delays the answer and can obscure what a clinician would otherwise have seen. No light source diagnoses anything, so a clinic that treats a changing mole as a cosmetic problem has skipped the step that mattered most.
Risks & Limitations
- Redness, warmth and swelling for hours to a few days after either light source; pigment often darkens before it flakes away over the following week.
- Purpura — a bruise-like change — with some picosecond wavelengths, taking a week or more to clear.
- Pigmentary change in the treated area, darker in most cases and lighter in some, particularly in darker skin types and after recent sun exposure.
- Blistering, crusting or a burn if the settings do not match the skin, and a small risk of scarring with either light source.
- A cold sore outbreak around the mouth after treatment in people who carry the virus.
- Results are not permanent. Sun-related pigment and redness recur, maintenance sessions are normal, and no course makes the change permanent.
- A lesion that has not been identified should be assessed, and in some cases sampled, before any light treatment; light does not diagnose.
- No outcome is guaranteed, and individual response varies with the lesion, the depth it sits at and the skin type.
When to Seek Care
- Blistering, crusting or a burn in the treated area — contact the treating team the same day.
- Rapidly increasing redness, swelling, pain or warmth, or discharge from the treated area.
- A fever, or a cold sore outbreak around the mouth after treatment.
- New or changing pigmentation in the treated area that is not settling as expected.
- A lesion anywhere on the skin that is new, changing in size, shape or colour, bleeding, itching or failing to heal — seek assessment rather than treatment.
- Difficulty breathing, or swelling of the lips, tongue or throat — seek emergency care immediately.
References & Further Reading
- American Academy of Dermatology Association (AAD) — patient information on laser and light-based treatment
- British Association of Dermatologists (BAD) — guidance on laser and light therapy
- National Institute for Health and Care Excellence (NICE, UK) — relevant guidance on skin lesions and referral
- Cochrane Library — systematic reviews in laser and light treatment of pigmented and vascular lesions
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.