Tattoo Removal and Q-Switched Lasers
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Direct answer
Tattoo removal uses Q-switched lasers, which deliver nanosecond pulses that the ink particles absorb and fragment through selective photothermolysis. The laser wavelength must match the ink colour, since black ink absorbs widely while red and yellow ink respond to green light at 532 nm. The fragments are then cleared by macrophages over several weeks, so removal requires repeated sessions.
What you must remember
- Selective photothermolysis: the ink, acting as the chromophore, absorbs the light, and the pulse is shorter than the thermal relaxation time, so surrounding skin is largely spared.
- Q-switching: the nanosecond pulse produces photomechanical stress that breaks the ink into smaller particles.
- Black and dark blue ink: the 1064 nm Nd:YAG laser is the usual choice, because these pigments absorb across the spectrum.
- Red and yellow ink: the 532 nm frequency-doubled Nd:YAG laser, which emits green light, is used for these pigments.
- Green and blue ink: wavelengths such as 694 nm from a ruby laser or 755 nm from an alexandrite laser are used, though responses vary.
- Clearance: macrophages carry the fragments away over weeks, so several sessions, usually spaced weeks apart, are needed.
- Picosecond lasers: shorter pulses fragment ink with less heat and are increasingly used, particularly for resistant colours.
- Endpoint: immediate whitening of the treated tattoo, called frosting, shows that the pigment has been fragmented.
Choosing the wavelength by ink colour
Wavelength choice is the central decision in Q-switched tattoo removal, because each colour absorbs a different part of the spectrum. The table lists the commonly used matches.
| Ink colour | Common wavelength | Comment |
|---|---|---|
| Black | 1064 nm Nd:YAG | Absorbs widely and is the most responsive colour |
| Dark blue | 1064 nm Nd:YAG | Responds well in most cases |
| Red or yellow | 532 nm Nd:YAG | Green light is absorbed by these pigments |
| Green or blue | 694 nm ruby or 755 nm alexandrite | Often more resistant and may need more sessions |
Multicoloured tattoos are treated with more than one wavelength, often in separate sessions, and the response is judged over the first few treatments. A test patch is sensible before a large tattoo is treated, because individual inks behave unpredictably.
Ink depth and composition vary between artists and inks, so some tattoos respond slowly even with the correct wavelength. Patients should be told that pigmentary change, such as lightening or hypopigmentation, can follow treatment, and that complete clearance is not always possible.
Where the exam tries to catch you
Stems on tattoo removal test whether you match the wavelength to the ink and recognise patients who are at risk of scarring.
- Trap: using one wavelength for every tattoo colour. Correct: ink colour determines the wavelength, so black, red and green pigments need different laser settings.
- Trap: using continuous or long-pulsed light to remove ink. Correct: Q-switched nanosecond or picosecond pulses are needed for photomechanical fragmentation without heavy thermal damage.
- Trap: treating a tattoo in a patient with a keloid tendency without caution. Correct: keloid-prone patients face a scarring risk, so a test area and careful counselling come first.
Frequently asked questions
Why does Q-switched laser removal need several sessions?
Q-switched lasers break tattoo ink into fragments, but the body clears those fragments through macrophages, which takes weeks. Repeated treatments, usually spaced several weeks apart, are needed to clear the ink progressively, so complete removal is rarely achieved in a single session.
Which laser wavelength is used for black tattoo ink?
The 1064 nm Nd:YAG Q-switched laser is the usual choice for black tattoo ink, because black pigment absorbs across the spectrum. Dark blue ink also responds well to this wavelength, while red and yellow ink need 532 nm light.
What does frosting mean during tattoo laser treatment?
Frosting is the immediate whitening of the treated tattoo that occurs when the laser delivers adequate energy to the ink. It is used as an endpoint, showing that the pigment has been fragmented.
Why are picosecond lasers used in tattoo removal?
Picosecond lasers deliver shorter pulses that fragment tattoo ink with less heat, and they are increasingly used for resistant colours. They are often considered when nanosecond Q-switched treatment has given a limited response.