Carbon dioxide lasers

The mainstay for skin resurfacing for the past few decades has been the CO₂ laser. Developed in the 1960s and implemented in the 1980s, the CO₂ laser has largely replaced deep phenol peels and mechanical abrasion⁷. CO₂ lasers emit light at a wavelength of 10600 nm that is strongly absorbed by water (the primary chromophore for CO₂ light abundant in the skin). Conversion of radiant energy to heat at the point of absorption instantly raises the temperature of tissue water to more than 100°C, so that the tissue water evaporates^7, 8. The CO₂ laser accurately evaporates the epidermis and dermis, resulting in the reorganisation and strengthening of collagen bundles in addition to epidermal regeneration to rejuvenate the skin.

The first CO₂ lasers developed used a continuous wave; however, this technique was not adopted widely owing to significant thermal damage and the high risk of scarring. The advent of short-pulsed high-energy and scanned CO₂ lasers that limit skin heating revolutionised the resurfacing industry.

These new lasers are capable of removing layers of photodamaged skin in a precise fashion, leaving only a narrow zone of thermal necrosis. The first laser pass significantly ablates more tissue than the second or subsequent passes, and an ablation plateau is reached at three to four passes, limiting depth to approximately 250 μm. The ability to control the epidermal vaporisation depth with minimal damage to the papillary dermis is a pre-requisite for successful, scorch-free skin resurfacing. The CO₂ laser achieves the desired results by removing the outermost layer of the epidermis and some portion of the superficial dermis, and then re-establishing this layer through normal wound healing. Healthy epidermis migrates from adjacent tissue and adnexal structures, and new collagen and elastic tissue are deposited by activated fibroblasts⁹. To respond to these requirements and achieve well-controlled tissue ablation without the risk of scarring or dyspigmentation, it is important to confine ablation to a thin layer (20–50 μm) and deliver enough energy to vaporise the tissue (5 J/cm²) in a time shorter than the thermal relaxation time of the skin (1 ms).

Two different types of CO₂ lasers are promoted for the purpose of skin resurfacing. The first is a high-power, pulsed CO₂ laser that can deliver a treatment fluency of 5–7 J/cm² with each sub‑millisecond pulse. The second uses an opto‑mechanical flash scanner connected to a conventional continuous-wave CO₂ laser. Later, CO₂ resurfacing lasers with short pulse durations (60 microseconds) emerged, which ablate less tissue per pass and leave a narrower zone of thermal necrosis than the original CO₂ resurfacing lasers. These newer systems allow epidermal vaporisation with minimal thermal damage to the papillary dermis. The newer super-pulsed lasers have pulse energies 5–7-times higher than conventional super-pulsed lasers to maximise tissue vaporisation. This results in pure steam vaporisation with minimal thermal injury diffusing to adjacent tissue.

As with other resurfacing modalities such as chemical peels and dermabrasion, CO₂ lasers completely remove the epidermis and part of the dermis, resulting in wound remodelling with the subsequent formation of new collagen and elastin fibre formation, creating firmer and tighter skin. Studies have shown that the depths of ablation are 20–30 μm and 30–50 μm after one pass using pulsed and scanning laser technology, respectively^10, 11. The residual thermal damage is 20–40 μm per pass, which does not increase to more than 150 μm on the third pass. The thermal damage produced by the newer CO₂ lasers can be controlled by varying the pulse duration, which makes the treatment safer, more reproducible, and more predictable.

Patient selection

It is advised to avoid resurfacing of any kind in Fitzpatrick skin types IV and higher, and also to those patients who have been taking Accutane for at least 1 year prior to treatment. In addition to the indications and contraindications, choosing between non-ablative fractional and ablative fractional devices will require some discussion with regard to lifestyle and down time. While non-ablative treatments tend to require multiple sessions with 1 day of downtime per session, ablative treatments generally require only one session with 48 hours of healing and up to 5 days of downtime.