Mechanism of laser acne treatment and laser tissue interaction

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Laser – tissue interaction and mechanism of laser acne treatment

The overall benefit of lasers and laser acne treatment is achieved via controlled and selective thermal damage and the fast delivery of the laser energy to the target tissue. It just takes 1 millisecond for successful laser acne treatment, the only time that is needed for tissue vaporization. Another benefit of laser acne treatment is the great precision that can be associated with procedures, laser acne treatments and other laser resurfacing treatments ensure minimal damage to the non-selective tissue of the skin and are therefore superior to other skin resurfacing treatments such as dermabrasion or chemical peeling.

The ability to control the epidermal vaporization depth with minimal damage to the papillary dermis is in fact the cause for the great success achieved by the new char-free, facial skin resurfacing laser resurfacing modalities for the photo-damged skin and the laser acne treatment.

For a well-controlled laser acne treatment and tissue ablation, without the risks of scarring or dyspigmentation, it is important to confine the ablation to a thin layer of skin (20–50 µm) and deliver enough energy to vaporize tissue (5 J/cm2) in a time shorter than the thermal relaxation time of the skin (1 ms).

To meet these requirements and achieve the desired results, the use of two different types of lasers is generally made, one which causes both the thermal damage and ablation and the second which causes only ablation.

Biological effects of the lasers

Unlike chemical peels and dermabrasion which produce abrasive damage, laser treatments with a CO2 laser entirely depend upon thermal damage. Heat that is generated results in immediate skin tightening because of shrinkage and denaturation of type I collagen in the skin. Fibrillar type 1 collagen undergoes helix-coil transition, which forcefully shortens the collagen fibrils by 30%. The collagen subsequently undergoes denaturation and sloughs off in a matter of days (17–20).

The new collagen formation (fibroplasia) that is achieved after laser treatment is thought to be dependent on the depth of the zone of thermal damage. Therefore, the degree of thermal damage (not the depth of tissue ablation) following laser resurfacing is very important for long-lasting clinical improvement, be it with laser acne treatment or laser resurfacing for the photo damaged skin.

It has been shown that the new-generation of carbon dioxide lasers allow a much more precise level of ablation (more focused ablation) and are more successful in the treatment of photodamaged skin and scarring compared to other types of laser.

These newer, super pulsed lasers help in maximizing the tissue vaporization because they have pulse energies five to seven times higher than conventional super pulsed lasers. The fast tissue vaporization also helps the new lasers to maintain a pulse duration of less than 1 ms. Since this pulse duration is less than the thermal relaxation time of the skin, these lasers are easily able to follow the principles of selective photothermolysis.

This results in pure steam vaporization of the skin with minimal thermal injury diffusing into adjacent tissue. Histopathologic studies have shown that around 20–30 µm and 30–50 µm depths of ablation were achieved after one pass using pulsed and scanning laser technology, respectively. The residual thermal damage was 20–40 µm per pass, which did not increase to more than 150 µm even when a third pass with the lasers was performed.

The residual thermal damage produced by novel CO2 laser technology is controlled by a shortening of the pulse duration, and produces controlled heating of the dermis. It seems that controlled dermal heating is very important for good clinical and histologic results in the treatment of photodamaged skin.

During the procedure, the thermal effect accounts for visible collagen shrinkage and immediate tightening of the skin. Observations under the microscope have shown that CO2 laser treatment leads to the formation of granulation tissue by day 30 after treatment.

The benefits of CO2 lasers continue long after the procedures are performed. The denatured, and therefore shortened collagen formed as a result of laser treatment acts as a matrix for new collagen to form. This remodeling process continues for many months as the thermally generated wound matures. Though laser tissue heating has been controlled to some extent by the depth of ablation, and the CO2 laser has been shown to give predictable results, there still is some potential for side effects from the thermal injury.

To avoid these thermally induced side effects, the use of a erbium:yttrium aluminum garnet (Er:YAG) laser with its higher affinity was sought and the ablation was achieved with minimal residual thermal damage. This system with a fixed short pulse width was popular for several years until it became apparent that the tightening effect on the skin achieved by this laser was less than that seen with CO2. This type of laser is now mostly used for laser acne scar removal treatment.

Comparisons to other procedures

Studies have shown that the resurfacing results achieved using new resurfacing CO2 lasers are safer and more predictable than mechanical dermabrasion and deep chemical peeling.

An animal study comparing CO2. lasers, phenol, trichloroacetic acid, and dermabrasion, has shown that the time required for healing for phenol treated skin was three times longer than with treatment using CO2 lasers because of deeper wounding and slower re-epithelialization.

Another comparative study of the treatment of periorbital wrinkles has confirmed that the results of treatment with CO2 lasers showed a statistically significant superior result compared with medium depth chemical peeling, though the time-duration of post-treatment erythema is longer (average, 4.5 months as compared to 2.5 months of medium depth chemical peeling)

All the results and the mechanism of action of laser acne treatment point towards the fact that laser re-surfacing is a superior technique compared to most other treatments.

1.E. Papadavid,and A. Katsambas, “Lasers for facial rejuvenation: a review”, 2003, The International Society of Dermatology, 42, 480–487
2.D. Railan, and S. Kimlmer, “Ablative treatment of photoaging”, Dermatologic Therapy, Vol. 18, 2005, 227–241

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