Pigment Lasers: Which Dark Spots Do Q-Switched and Picosecond Lasers Work On, and Why Is Caution Needed with Melasma?

What is a pigment laser and how does it work?

Melanin, the pigment that gives the skin its colour, absorbs light of particular wavelengths. Pigment lasers deliver this light in very short pulses, on the scale of a billionth of a second (a nanosecond) or a trillionth of a second (a picosecond). The pulse is so short that the energy is concentrated in the pigment granules, breaking them into small fragments, before it has time to spread to the surrounding tissue. Part of the fragmented pigment is shed from the skin within days in a fine crust, and part is cleared over weeks by the body's scavenger cells.

• Q-switched lasers: deliver pulses on the nanosecond scale. This is the group that has been used for many years and about which the most has been published.
• Picosecond lasers: deliver even shorter pulses. They were first developed for removing tattoos and later came to be used for pigmented marks as well.

Both groups include different wavelengths. Short wavelengths target pigment at the surface of the skin, and long wavelengths pigment that lies deeper; for this reason a different laser is chosen according to the type and depth of the mark. The use of the same lasers on tattoo ink is explained in the article “Laser Tattoo Removal”.

A device's advertised name, or its being 'new generation', does not show that it is suitable for your mark. What you need to ask is what the diagnosis of your mark is, which technology and wavelength the device works with, and whether it is used on your skin type.

Diagnosis first: which marks should not be lasered?

Not everything that looks brown on the skin is the same thing. A sun spot, a freckle, melasma, a mark left after a spot, a birthmark and a mole can resemble one another; yet each is a different structure and responds differently to laser. More importantly, melanoma, a type of skin cancer, can also look like an ordinary spot or mole at first glance.

Laser breaks up pigment, but it does not send tissue for examination. If laser is used on an undiagnosed mark, the appearance of the lesion changes, no tissue has been obtained for examination, and the true diagnosis may be delayed. For this reason laser is not used on moles, or on marks that are changing in shape, colour or size, have irregular borders, have newly appeared or look different from the others; an examination by a dermatologist comes first, with examination using a magnifying instrument (a dermatoscope) and a tissue sample if needed.

What each type of spot, mole or skin tag means, and which need to be examined, is explained in the article “Moles, Skin Tags and Spots”. For the types of pigmentation and the warning signs of melanoma, you can also see the article “Dark Spots and Melasma”.

Which marks does it work on?

The responses in this table show general tendencies; how your mark will respond is assessed during the examination. A review of lasers for café-au-lait spots reports that most of the mark cleared in fewer than half of patients, and that the mark came back in about one in eight patients; the quality of evidence of the studies included in the review is low. For naevus of Ota, a review bringing together 57 studies concluded that the option with the most data is the Q-switched Nd:YAG laser.

Why is caution needed with melasma?

Melasma is a long-term condition in which the pigment cells have become over-sensitive to sun, heat and hormones. Laser can break up the existing pigment, but it does not change this sensitivity of the pigment cells. A review of laser and light treatments for melasma reports that the methods used appear effective in the short term, but that the rate at which the pigmentation comes back over time is high and that some techniques increase the risk of darkening or lightening of the skin after the procedure.

One of the methods most often used for melasma is the Q-switched laser applied at low energy, over a wide area and at frequent intervals in a large number of sessions. After this treatment, small speckled areas lighter than the surrounding skin have been reported to develop on the face. A case series of 14 people published from Hong Kong reports that these people had received between 6 and 50 sessions, that the lightening could sometimes appear after only a few sessions, and that against a background of melasma it could lead to marked disfigurement. In the same series, no meaningful improvement in the pigmentation was achieved in five people treated for melasma.

In some people the light-coloured speckles may be long-lasting or may not reverse. How often such cases occur is not known; the data are based on case series. For this reason, in melasma laser is considered only in selected people in whom sun protection and cream treatments have not given a sufficient result, in a limited number of sessions and by an experienced physician. Be cautious about 'skin tone evening' or 'brightening' programmes sold as packages of dozens of sessions.

Why is the risk higher in dark and tanned skin?

Laser does not distinguish between the pigment in the mark and the skin's natural pigment. The darker the skin's own colour, the greater the share of the light that is absorbed by pigment that is not the target. The result is a darkening that appears weeks after the procedure and may be wider than the treated mark; in medicine this is called post-inflammatory hyperpigmentation.

Small comparative studies of sun spots in Asian patients give an idea of the size of this risk. In a study of twenty people, a Q-switched laser was used on one half of the face and a picosecond laser on the other; darkening after the procedure was seen in about one in three people on the Q-switched side and in one in twenty on the picosecond side. In another study, darkening developed in eight of 17 patients with sun spots treated with a Q-switched laser, while none developed on the side treated with IPL. These studies are small, their follow-up periods are short and they were carried out with different devices; they should not be read as a rate for your own risk.

Tanned skin behaves in the same way; the procedure is generally postponed until the tan has faded. Assessment of skin type, test spots and choice of device are dealt with in detail in the article “Laser, IPL and Chemical Peels on Olive and Darker Skin”.

Who is it not suitable for, and what should you watch out for?

• Undiagnosed or changing marks and moles: an examination is needed first.
• Tanned skin; recent sun exposure, sunbed use or use of self-tanning products
• Dark skin and a history of marks remaining after wounds, spots or procedures: the risk is high; the decision rests with the physician.
• Melasma: not the first choice, for the reasons explained above.
• Medicines and herbal products that cause sensitivity to light: report everything you use; do not stop your medicine on your own.
• An active cold sore, infection, open wound or flare of a skin condition in the treatment area
• Conditions involving loss of colour, such as vitiligo: laser can trigger new areas of colour loss.
• Pregnancy: the procedure is generally postponed because there are not enough data on its safety and the tendency to pigmentation increases in pregnancy.
• A tattoo in the area, or cosmetic pigment in areas such as the lips or eyebrows: the pigment can change colour unexpectedly.

Who should perform it, and where?

With pigment lasers, the first step that determines safety is not the device but the diagnosis. Telling whether a mark is a sun spot, melasma or a mole that needs to be examined is a medical assessment. For this reason it is recommended that the diagnosis and the treatment decision be made by a physician with knowledge of skin diseases and that the procedure be carried out under a physician's responsibility. The general framework on who is authorised is explained in the article “Who Can Perform Medical Aesthetic Treatments?”.

The light from these lasers can cause serious and irreversible eye damage if it reaches the eye without protection. Everyone in the room needs to wear protective eyewear suited to the wavelength being used.

Preparing for the procedure

• The mark is diagnosed during the examination; the physician may examine it with a dermatoscope and, if considered necessary, take a tissue sample first.
• Protect yourself from the sun in the weeks before the procedure; do not use sunbeds or self-tanning products. Your physician will tell you how long is needed.
• Report the medicines and herbal products you take and the products you apply to your skin. Ask your physician when to pause retinoids, acid-containing products and peels.
• Be sure to mention any history of cold sores and any pigmentation or burn you have had after laser, light or peel treatments.
• Your physician may wish, particularly in dark skin, to treat a small test spot first and see how the skin reacts over the following weeks.
• On the day of the procedure there should be no make-up, perfume or sunscreen on the area.

The day of the procedure, step by step

1. Your medical history and expectations are reviewed; the informed consent form is read and signed. Photographs are usually taken for the record.
2. The skin is cleaned. Your eyes and those of everyone in the room are protected with suitable protective eyewear or eye shields.
3. A numbing cream or cooling is used if needed; for small spots it is usually not required.
4. The laser handpiece is held over the mark and the pulses are delivered. With each pulse there may be a brief sensation like the snap of a rubber band and a crackling sound.
5. With superficial marks such as sun spots, a grey-white colour that disappears within minutes may appear over the mark immediately after the pulse; the physician watches for this as a sign of response to the treatment.
6. The area is cooled, a protective cream is applied and aftercare advice is given. You can go home the same day.

After the procedure: the first 24 hours, the first week, the first month

• First 24 hours: there may be redness, mild swelling and a feeling of warmth similar to sunburn. A cool compress may be soothing; do not apply ice directly to the skin. Avoid hot showers, saunas, Turkish baths and intense exercise.
• First week: the treated spots darken and form a fine crust. This is expected; do not scratch or rub the crusts, and wait for them to fall off by themselves. Use a gentle cleanser and the moisturiser or cream your physician recommends.
• First month: after the crust has been shed, the skin beneath may look pink or lighter than the surrounding skin for a while. Use a broad-spectrum sunscreen every day, and do not neglect a hat and shade.
• If weeks later you notice new darkening in the treated area, do not apply a pigment cream on your own; tell your physician.

How to choose a sunscreen and how often to reapply it are explained in the article “Sunscreen Guide”.

Expected side effects and emergency signs

• Redness, mild swelling and a feeling of warmth: usually lessen within hours to a few days.
• Darkening and fine crusting of the spots: mostly shed within a week or two.
• Pinpoint bleeding or bruising: may be seen with some settings and passes within days.
• Temporary pinkness or lighter colour after the crust has been shed

Less commonly, darkening or lightening of the skin after the procedure, blistering, burns, a cold sore flare-up, infection and scarring may occur. Colour changes usually improve over months; in some people, however, they may last a long time or may not reverse. The signs of these problems, what to do at home and the treatment options are explained in detail in the article “Burns and Pigmentation Changes after Laser and IPL”; we do not repeat them here.

How many sessions are needed, and when is the result seen?

With sun spots and freckles, the first change is noticed when the darkened spot is shed within a week or two. Most comparative studies have assessed the effect of a single session; some spots may need a second session. For birthmarks, treatment is much longer and sessions are repeated weeks or months apart. The number of sessions is determined by the type and depth of the mark, your skin type and how the skin responds.

How long the result lasts depends on sun protection. Even if a treated sun spot clears, new spots form as long as sun damage continues; freckles reappear with sun. In melasma and café-au-lait spots, the mark coming back in the same place is a common occurrence.

Is picosecond laser superior to Q-switched laser?

A comprehensive review of picosecond lasers reports that there is evidence, of a quality that varies from study to study, supporting their use for benign pigmented marks, while in melasma the evidence is more limited. In the small study mentioned above, the picosecond laser was found both to be more effective on sun spots and to cause less darkening. This is a single, small study.

In short, there are data suggesting that picosecond laser may be superior in some situations, but this has not been shown for every mark and every skin type. The result is determined less by the name of the device than by the right diagnosis, the right wavelength and cautious settings.

How does it differ from IPL?

Which is suitable varies with the type and number of marks, any accompanying redness and the skin type. Who IPL is suitable for and what the procedure involves are explained in the article “IPL (Intense Pulsed Light) for Dark Spots and Redness”.

Realistic expectations: what can a pigment laser not do?

• It does not prevent new spots from forming; it does not replace sun protection.
• It does not eliminate melasma; in some people it can make it worse.
• It does not erase every mark in a single session and without a trace; some marks only lighten.
• It does not show whether a mark is benign; it does not make a diagnosis.
• It does not correct wrinkles, sagging or the appearance of pores.
• No promise can be made about the result; the same laser gives different responses in different people.

Alternatives

Peel options are dealt with in the article “Chemical Peels”. Which method suits you should be decided together with your physician, who determines the type of mark on examination.

This content is for information purposes; it does not replace an examination.