In short. Neither light source stops the process behind the problem. Why pigment and redness return, what maintenance does, and why sun protection is part of the result.

Key points

  • Follow-up sessions are usually scheduled rather than offered as a repair for failure.
  • Their purpose is to deal with what has reappeared since the last treatment, at a smaller scale than the original course, and they are the mechanism by which a result is held rather than the sign that the treatment did not work.
  • A patient who knows this in advance reads a maintenance session as routine.

Light-based treatment removes what has accumulated; it does not turn off what produced it. That single sentence explains most of the disappointment patients report a year later, and it is worth understanding before a course starts rather than after it finishes.

What the underlying process does

Sun-related pigment forms because melanin-producing cells respond to ultraviolet exposure. Small superficial vessels dilate and become visible for reasons that include sun damage, temperature, hormones and genetics. Targeting the visible result does not change the tendency that produced it. Freckles and sun spots return with further exposure, often in the same places, because the skin that produced them is the same skin. Redness returns as vessels respond again. Hormonal pigment, driven by something other than light exposure alone, returns most readily of all. Tattoo ink is the clear exception: once the particles have been cleared, they do not come back in that area.

Maintenance is part of the plan, not a relapse

Follow-up sessions are usually scheduled rather than offered as a repair for failure. Their purpose is to deal with what has reappeared since the last treatment, at a smaller scale than the original course, and they are the mechanism by which a result is held rather than the sign that the treatment did not work. A patient who knows this in advance reads a maintenance session as routine. A patient who does not reads it as evidence of failure, and those are the same appointment.

What makes a result hold longer

Daily sun protection is the largest single influence on how long a pigment or redness result lasts, and it applies to both light sources equally. Avoiding deliberate tanning, staying out of the sun during the healing period, and treating pigment while the skin is settled rather than immediately after a holiday all improve how long the change holds. Beyond that, duration depends on the lesion, the depth it sat at, the skin's own tendency to pigment, and how many sessions were completed. None of that can be promised in advance, and a clinician who gives a number of years is guessing.

Where expectations go wrong

  • A result treated as permanent. Pigment and redness recur in most people, and maintenance is normal rather than a sign that something failed.
  • Overlapping treatments stacked into one period. Energy delivered to skin that has not recovered raises the risk of a pigmentary change instead of accelerating the result.
  • New or changing pigmentation read as recurrence. A lesion that is new, changing or unusual is assessed before it is treated again, because treating it is not the same as examining it.

The honest summary

Both light sources give a real change that is held by maintenance rather than by the treatment alone. That is not a weakness peculiar to either one; it is how light works on skin that continues to live in the world. Knowing it in advance turns a future appointment into routine care instead of a disappointment.

Related reading

Frequently asked questions

Will the pigment or redness come back?

In most people, yes. Light treatment removes what has accumulated; it does not switch off what produced it. Sun-related pigment returns with further exposure, often in the same places, because the skin that produced it is the same skin. Redness returns as vessels respond again. Hormonal pigment returns most readily of all. Tattoo ink cleared by picosecond pulses is the exception: it does not come back in that area.

Are maintenance sessions a sign the treatment failed?

No. They are usually scheduled rather than offered as a repair, and their purpose is to deal with what has reappeared since the last treatment at a smaller scale than the original course. That is the mechanism by which a result is held, not evidence that it did not work. A patient who knows this in advance reads a maintenance session as routine, and a patient who does not reads it as failure, even though it is the same appointment.

What makes a result last longer?

Daily sun protection is the largest single influence, and it applies to both light sources equally. Avoiding deliberate tanning, staying out of the sun while the skin heals, and treating pigment when the skin is settled rather than straight after a holiday all help. Beyond that, duration depends on the lesion, the depth it sat at, the skin's tendency to pigment and how many sessions were completed. None of that can be promised in advance.

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

Medically reviewed by Ke He, MD (何锞), Deputy Director & Head of Skin & Laser Aesthetics. Last reviewed: 19 September 2026.

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.