One of the most common requests in aesthetics is the removal of ‘Brown spots’ and other pigmented lesions. Because all pigmented lesions contain the light absorbing pigment melanin, lasers are often used to selectively target pigment, whilst sparing surrounding normal structures.
Melanin is produced by specialist skin cells within the epidermis called melanocytes. These cells insert granules of melanin into tiny structures within the cell called melanosomes. Melanocytes are branched cells with finger like projections. As the melanosomes mature, they migrate to the tips of the projections and are transferred into the surrounding skin cells.
The complex choice of which laser to use in the treatment of a pigmented lesion is often taxing for the most experienced laser physician. It depends on numerous factors including the type and depth of lesion, its size and location, the patient’s underlying skin type and other variables.
By selecting the appropriate laser wavelength (colour) and pulse width (dwell time) a pigmented lesion can be destroyed with little or no injury to normal surrounding skin.
Effect of pulse width (dwell time)
The time a laser beam remains or dwells on a particular area is very important. Medical lasers usually deliver energy in pulses, typically in the nanosecond (ns) or millisecond (ms) range. A pulse of light with a wavelength absorbed by the pigmented lesion that dwells on the target just long enough to heat the target, cutting off before any heat is allowed to transfer to normal adjacent tissue, will destroy the target and spare the surrounding structures. The pulse width needs to shorter than the thermal relaxation time (the time required for an object to cool to half the temperature) of the structure. The length of the pulse width is roughly proportional to the size of the target.
If the target is very small (intracellular melanosomes) a Q switched laser with a pulse width of nanoseconds will best match the thermal relaxation time, destroying the stored pigment, leaving the melanocytes which are producing the melanin relatively undamaged.
When the aim is to destroy larger melanin containing cellular structures a millisecond pulse laser will best match the thermal relaxation time, allowing the heat energy to spill over from the stored pigment into the surrounding melanocytes and keratinocytes causing more extensive thermal damage.
If the pigmented part of the lesion is bulky or above the surface of the adjacent skin, a laser with a non–selective thermal effect such as the Er Yag 2940nm laser or CO2 10,600 nm laser might be the most appropriate choice
The effect of wavelength (colour)
Several different laser wavelengths can be used to selectively treat pigmented lesions, including green (KTP 532nm laser), yellow (PDL 595nm laser), red (Ruby 694nm laser and Alexandrite 755nm laser) and infrared (Nd Yag 1064nm laser)
Other components of the skin (blood and protein) also compete with melanin to absorb laser light, and as a result, shorter wavelengths (KTP 532nm and PDL 595nm laser) do not penetrate the skin as deeply as longer wavelengths.
A useful therapeutic window of wavelengths exists between 630nm – 1100nm where melanin absorption exceeds that of haemoglobin and laser light penetrates deeply.
As the absorption of melanin falls as the wavelength increases, higher fluences (power) are required at longer wavelengths to produce the same damage to the melanosomes.
To complicate matters, melanin normally present in the skin may compete with the melanin in a pigmented lesion, which can further limit the choice of wavelength in a given patient. The depth and relative content of melanin in the skin and pigmented lesion determines which laser wavelength is most appropriate for a given patient.
Our Cambridge Laser Clinic offers the complete range of laser and light technologies best suited to treat pigmented lesions, ensuring optimal results.
- Ruby 694 nm Q switched laser
- Alexandrite 755nm LP laser
- KTP 532 nm Q switched laser
- Nd YAG 1064nm Q switched laser
- IPL 540 – 950nm light source
- IPL 570 – 950nm light source
- Er Yag 2940nm laser
- C02 10,600nm laser
A full medical consultation is essential for diagnosis, confirmation and exclusion of pigment problems associated with malignancy such as melanoma. At our Cambridge Laser Clinic all consultations for pigmented lesions are carried out by a doctor.