D G C © 2008

Updated May 08

SAJJAD F RAJPAR, SEAN W LANIGAN

Lasers have been used in dermatology for over 30 years. During this period, the collaboration of clinicians, scientists and manufacturers has facilitated the development and refinement of laser devices with improved safety and efficacy. In this article, we discuss the basic principles of lasers and their main uses in dermatology. We also provide other practical advice.

Basic Principles

Lasers deliver powerful and short bursts of light of a single wavelength. The wavelength determines the colour of light emitted. Most dermatologic lasers produce light in the ultraviolet, visible or infrared spectrum. The waves travel in synchrony and in parallel, allowing high energies to be focussed onto small spots. The light energy is absorbed by target structures in the skin and converted to heat energy, which produces the desired effect.

Different structures absorb different colours of light. By choosing the right colour, thermal damage is restricted to target structures so that surrounding structures can be spared. This important concept is known as “selective photothermolysis” – the selective heating of target structures by matching the wavelength of laser light with the absorption characteristics of the target. The main targets in the skin are oxyhaemoglobin, melanin, tattoo pigment, and water. They absorb different wavelengths of light to varying degrees. Sometimes, more than one laser is useful for a particular target. If a target is deeper in the skin, a laser with a longer wavelength may be chosen.

Another important parameter is the pulse duration, which is the duration of each laser shot. Small structures, such as tattoo particles, heat up quickly and need energy in small bursts that last a matter of nanoseconds. Larger structures, such as hair shafts, heat up more slowly and need energy in milliseconds, which are a million times longer than nanoseconds. Because of this, the same wavelength of laser light can have different effects on the skin depending on the pulse duration.

In certain situations, it is important to protect the epidermis (the top most layer of the skin) from laser energy, as the target is deeper in the dermis. This can be achieved by cooling the epidermis with cooled air, cryogen spray or a cold contact tip. Not all lasers require cooling.

Intense pulse light devices are not true lasers because they emit a whole range of light of different colours with every shot. However, the light works in the same way as with lasers in that it is absorbed by target structures and converted to heat. Because so many different wavelengths are emitted, several structures may be targeted all at once. IPL devices can be used for certain vascular lesions, pigmented lesions and hair removal, though there is a lack of comparative studies to establish how they compare to lasers.

Clinical uses

The 4 main areas that lasers are used for in dermatology are for vascular lesions, pigmented lesions, hair removal and resurfacing.

Vascular lesions

Vascular lesions are made up of blood vessels, and include thread veins on the face and legs, birthmarks such as port wine stains and haemangiomas, and general facial redness from conditions like rosacea. Lasers can be used to reduce the size and lighten the colour of vascular lesions. Sometimes, complete disappearance of the lesions can be achieved. 

A variety of lasers and IPLs can be used to treat vascular lesions. The target in this situation is haemoglobin in red blood cells within the vessels. Haemoglobin is selectively heated, causing damage to the lining of blood vessels and coagulation of blood, ultimately leading to shrinkage or loss of the blood vessel. Bruising that lasts up to a week is common after treatment.

Port wine stains are a type of birth mark that co0mprise abnormal vessels in the dermis, and affect 0.3% of the population. Treatment with the pulsed dye laser can achieve 60 to 80% lightening in most patients, and approximately 20% of lesions clear completely. Treatment can be delivered in infancy, and clearing lesions at this stage will prevent problems such as bullying at school age. Six to ten treatments delivered at 6 weekly intervals are usually required. On the other hand, red facial veins may only require one or two treatments.

Lasers used for vascular lesions

Wavelength                  Type of laser                            Main indications

532 nm                         KTP                                  Facial telangiectasias

585 or 595                   Pulsed dye                         Port wine stains, haemangiomas, Diffuse facial erythema

 1064 nm                     Long pulsed Nd:YAG        Leg veins                                               

 Various                      IPL                                      Telangiectasias, facial erythema                                  

Pigmented lesions

Pigmented lesions are dark marks on the skin that arise because there is too much melanin. The most common pigmented lesion treated with lasers is solar lentigos. These are also known as age or liver spots. Other pigmented lesions that respond well to laser treatment are freckles, café au lait macules and nevus of Ota (the last 2 are types of birthmark). Post inflammatory hyperpigmentation and melasma respond poorly.

Tattoos have been performed for over 4000 years, and it is estimated that at least 5% of adults have a tattoo. Tattoos acquired during teenage years are often regretted in adulthood. Black, blue, green and red pigment clears the best, with amateur tattoos often requiring only 3 or 4 treatments. The response is much more variable with yellow, brown, purple and white pigment, and multiple treatments may still not clear all the pigment.

The lasers used to treat melanocytic lesions and tattoos are Q (‘quality’)-switched, which means they deliver energy in nanoseconds so as to explode tiny pigment particles.

Lasers used for pigmented lesions

Wavelength                 Type of laser                                              Main indications

532 nm                      Q-switched frequency doubled Nd:YAG       Red tattoo pigment, lentigines

 694 nm                      Q-switched ruby                                          Lentigines, café au lait macules,

 755 nm                      Q-switched alexandrite                                 nevus of Ota, Black/blue/green

1064 nm                     Q-switched Nd:YAG                                   tattoo pigment

Various                      IPL                                                                Lentigines

Hair removal

This is the most popular laser treatment. Hair growth can be arrested by damaging the lining of the hair follicles. This is achieved by selectively heating hair shafts by targeting melanin within them. The heat damages the surrounding hair follicle. Melanin in the epidermis needs to be protected with cooling devices.

An average reduction in hair of 60 to 70% can be achieved with 6 treatments. Patients with dark hair and fair skin respond the best, though darker skin types can now be effectively treated with new lasers such as the long pulsed Nd:YAG. This laser is particularly useful for ingrown hairs leading to pseudofolliculitis barbae. Hair that is red, blonde or white, and very fine hair, usually respond poorly, if at all.

Lasers used for hair removal

Wavelength                     Type of hair

694 nm                         Long pulsed ruby

755 nm                         Long pulsed alexandrite

800 nm                         Long pulsed diode

1064 nm                        Long pulsed Nd:YAG (best for darker skin types)

Various                         IPL

often advertised as providing ‘permanent’ hair reduction. The FDA is responsible for approving medical devices in the USA. Their definition of permanent is 6 months, hence ‘permanent’ in the context of hair removal really means 6 months. It is usual for most patients to require one or two treatments a year to maintain the response they achieved.

Resurfacing

These lasers target tissue water, and peel layers off the skin. Precise peeling of thin layers of skin can improve the appearance of aging skin and acne scarring. Healing from laser resurfacing can take several weeks. Warts and non-melanoma precancers can also be treated with these lasers.

Lasers used for resurfacing

Wavelength                               Type of laser

2940 nm                                   Er:YAG

10600 nm                                 Carbon Dioxide

Lasers for cosmetic use

Vascular lasers, pigment lasers and IPLs are very effective at treating certain elements of sun damage including age spots, rough skin, and broken and dilated blood vessels. Wrinkles respond better to resurfacing lasers. Other treatments including fillers and muscle relaxing toxins are also useful for wrinkles and often need to be used in combination with lasers.

The field of dermatologic lasers continues to expand. New devices include the excimer laser which emits ultraviolet light and is useful for treating psoriasis, and to a lesser extent, vitiligo. However, not many units offer excimer laser treatment at this time.

A new fractional resurfacing laser that arranges the laser beam in a unique way that may allow resurfacing to be carried out with fewer side-effects has also become available. The effects are not as good as conventional resurfacing lasers, but healing is a lot quicker, and so this treatment is becoming popular.

Existing lasers, particularly the pulsed dye laser, are increasingly used as light sources for photodynamic therapy in the treatment of precancers of the skin.

The sensation of having a laser treatment is likened to the feeling of someone flicking a finger or a rubber band. Some lasers are more uncomfortable than others, though most people find it tolerable.

A test patch is often performed before a full treatment. This is a good opportunity to experience the sensations. If it is intolerable, anaesthetic cream can be applied before treatment.

Will anaesthetic be required?

Most laser treatment is carried out without any anaesthetic whatsoever. A general anaesthetic is used for laser resurfacing procedures, and for treatment of young children. In certain situations, local anaesthetic injections or creams are given.

One laser does not fit all

No single laser can be used to treat the breadth of dermatologic conditions. Multiple lasers are required, so that treatment can be tailored to individual needs with maximum efficacy and minimum side effects. An intimate knowledge of laser-skin interactions is necessary for laser operators, as incorrect use of lasers seriously increases the risk of permanent side effects such as pigment abnormalities and scarring. Laser services should therefore be sought from dermatologists or equivalently trained specialities.

Sajjad F Rajpar, Sean W Lanigan

Department of Dermatology

Birmingham Regional Skin Laser Centre

Birmingham Skin Centre, 3^rd Floor, Sheldon Block

Dudley Road,

Birmingham B18 7QH