Fractional photothermolysis uses an array of small laser beams to create many microscopic areas of thermal necrosis within the skin. These areas of necrosis are deemed microscopic treatment zones (MTZs). Fractional photothermolysis performed within these MTZs completely destroys the epidermis and dermis, but the necrotic injury heals rapidly and adverse effects are few. [1, 2] A large number of new devices have come onto the market, and their individual use must be assessed by the dermatologist individually. Nonablative laser resurfacing has been evolving away from scanning technology to fractional technology. 
With nonablative laser, it is difficult to cause a robust fibroplasia on a histologic basis and its ability to induce skin tightening yeilds clinically inconsistent results. 
Fractional resurfacing is an effective treatment for hypopigmented scarring on the face.  Collawn  treated 70 patients with abnormal pigmentation, wrinkles, or scars on their faces and/or extremities for with 2-6 treatments 1-3 weeks apart using the Fraxel laser (Reliant Technologies, Inc). Patients experienced erythema and edema for a few days, followed by light skin exfoliation for a few days, and noted a more even skin color and texture and a decrease in the unwanted melanocytic pigmentation and rhytides. Others have noted that fractional laser reportedly is a useful treatment for pigmentation and texture improvement. 
Fractional resurfacing has also been reported to be successful in the treatment of third-degree burn scarring. 
Pulsed char-free carbon dioxide laser skin resurfacing has provided a method of removing thin layers of skin with minimal thermal damage. These lasers improve mild, moderate, and severe rhytides, as well as photoaged skin. Laser energy is delivered at the ablation threshold of the skin, without the adverse effects seen with older, nonpulsed, continuous-wave carbon dioxide lasers. The presumed mechanisms of char-free pulsed carbon dioxide laser rhytid improvement are epidermal ablation, dermal damage with collagen remodeling, and thermal contraction.
Carbon dioxide laser resurfacing has been used successfully on nodular and hypertrophic components of port wine stains. 
Despite the clinical improvement seen after carbon dioxide laser treatment, the enthusiasm for this system has been tempered by the prolonged healing and significant erythema that commonly occurs following laser treatment. Although this erythema may resolve in 1 month, it commonly lasts up to 6 months. When experienced laser physicians perform carbon dioxide laser surgery, the results are excellent; however, the novice laser physician has not found carbon dioxide systems to be as user friendly. With this significant learning curve, some physicians have shied away from laser resurfacing.
The erbium:yttrium-aluminum-garnet (Er:YAG) laser, with its 2940-nm wavelength, emits laser energy in the mid-infrared invisible light spectrum. This wavelength has 10-15 times the affinity for water absorption compared with the carbon dioxide wavelength (10,600 nm). It is this fact that leads to the difference in clinical response observed after treatment with these 2 lasers. The Er:YAG laser wavelength is at the peak of water absorption. Er:YAG laser treatment leads to epidermal ablation and dermal remodeling. Unlike carbon dioxide lasers, these systems produce little thermal effect.
The Er:YAG laser is a true ablation laser. This laser is unlike carbon dioxide lasers, which cause both vaporization and desiccation. Both the Er:YAG laser and the pulsed char-free laser have water as the absorbing chromophore. The Er:YAG laser produces only about 5-20 µm of thermal damage per impact as opposed to the 50-125 µm of additional thermal damage observed with each pass of the carbon dioxide laser. Carbon dioxide lasers produce a significant thermal effect; this residual thermal damage becomes a heat sink for the next pass of the carbon dioxide laser. This damage leads to desiccated collagen with a resultant increase in new collagen production. Such an effect would not be expected after Er:YAG laser treatment.
The duration of erythema after Er:YAG resurfacing is usually less than with carbon dioxide laser treatment because Er:YAG laser treatment often involves more superficial ablation and leaves minimal thermal damage. Wound healing and recovery time following Er:YAG laser treatment is generally shorter, making it ideal for resurfacing relatively young people who lack deep wrinkles or extensive photodamage. However, a draining wound is still created with Er:YAG laser technology.
Both carbon dioxide laser and Er:YAG laser technology, although promising in their benefits, sometimes are accompanied by untoward adverse effects and complications. The most common of these, as mentioned above, is postoperative erythema, an adverse effect experienced by virtually all patients treated with these modalities. Other potential risks induced by ablative, dermal wounding modalities include delayed healing, postoperative pigmentary changes, and scarring.
If a dermal wound and new collagen formation is the primary mechanism behind the improvement seen after laser resurfacing, techniques that induce a dermal wound without epidermal ablation theoretically should lead to cosmetic improvement of dermal photodamage. This arena of nonablative dermal remodeling is a new area of laser technology.
Handley et al  noted that adverse events can occur with nonablative cutaneous visible and infrared laser treatment.
Recent studies have shows that Fitzpatrick skin types IV to VI lasered with a 1,550-nm erbium-doped fractional type nonablative laser had a low incidence of treatment-related pigmentary alteration. 
It seems clear that nonablative laser has a place in the treatment of patients who are younger than 50 years and have nonsagging skin; it can yield results similar to ablative procedures in such patients. 
Finally, nonablative lasers have a place in improving the appearance of scars and grafts in patients after Mohs micrographic surgery. 
The dual-spot-size carbon dioxide ablative fractionated laser has been used effectively to treat acne, with few of the adverse effects of a truly ablative laser. 
Weiss et al  noted that based on a prospective clinical evaluation, 1440-nm laser treatment delivered by microarray is effective for treating photoaging and scars, specifically inducing neocollagenesis in the remodeling of scars and rhytides.
Trellas et al  noted that no single nonablative laser can achieve all the specific effects needed for effective skin rejuvenation, and they suggest that combinations of treatments are the most useful modes of treatment. Fractional resurfacing has largely replaced other ablative technologies, and nonablative techniques have become more widespread.
Although nonablative treatments are useful, they are still not as effective as ablative treatments. This was highlighted in a study by Ong and Bashir; ablative fractionated laser induced an improvement range between 26-83% whereas nonablative fractionated laser had an improvement range between 26-50%. 
Also see the Medscape article Nonablative Facial Skin Tightening.
History of the Procedure
In one of the first studies evaluating a nonablative approach to dermal remodeling, a 1064-nm Q-switched neodymium:yttrium-aluminum-garnet (Nd:YAG) laser was used in an attempt to improve rhytides. Eleven research subjects with perioral or periorbital rhytides were treated with a Q-switched Nd:YAG laser at 5.5 J/cm2 and a 3-mm spot size. All research subjects had skin phenotypes I and II, and all had class I or II rhytides. The authors sought a nonspecific clinical endpoint of pinpoint bleeding, as demonstrated in the image below.
The research subjects were treated only once and were evaluated 7, 30, 60, and 90 days after treatment. At follow-up, each research subject was evaluated for improvement of rhytides, healing, pigmentary changes, and erythema. In 3 patients (2 perioral and 1 periorbital), the authors noted improvement that was thought to be comparable to that following ablative resurfacing. In 6 patients (3 perioral and 3 periorbital), clinical improvement was noted but was not thought to be as significant as that observed with an ablative laser system. In 2 patients (1 perioral and 1 periorbital), no clinical improvement was noted. In those research subjects where clinical improvement was noted, the clinical changes were consistent the full 90 days of the study. No pigmentary changes or scarring was noted in any of the treated research subjects. At 1 month, 3 of the 11 research subjects showed persistent erythema at the treated sites. At 3 months, all erythema was resolved.
Dermal remodeling is thought to occur through increased collagen I deposition with collagen reorganization into parallel arrays of compact fibrils. Such an effect, the authors suggested, might occur with nonablative laser systems as well as ablative laser systems. Of note, the greatest improvement occurred in individuals who had the most persistent erythema. This finding suggested that the degree of improvement following any dermal wounding approach might be directly related to the degree of induced wound.
This study was expanded when the nonablative dermal remodeling effects of a Q-switched Nd:YAG laser was potentiated by the use of a topical carbon-assisted solution. Two hundred forty-two solar damaged anatomical sites on 61 human subjects were treated with three 1064-nm Q-switched Nd:YAG laser treatments. Parameters of treatment included a fluence of 2.5 J/cm2, pulse duration of 6-20 nanoseconds, and a spot size of 7 mm. The treatment sites were evaluated at baseline, 4, 8, 14, 20, and 32 weeks for skin texture, skin elasticity, and rhytid reduction. All sites were treated at a baseline visit and later at 4 and 8 weeks. Adverse events were recorded throughout the study.
In this study, a low fluence Q-switched Nd:YAG laser was used for treating mildly solar-damaged skin. Unlike the previous study, no epidermal disruption occurred when the lower fluences were used. The Q-switched Nd:YAG laser energy is not well absorbed by tissue water; it is nonselectively placed within the dermis. The 1064-nm wavelength results in relatively deep penetration into the skin, which is indicative of minimal laser-tissue interaction. As a result, cellular damage is localized to the tissue immediately adjacent to the carbon, nontargeted tissue is minimally affected, and less than 10% of the typical energy output from carbon dioxide lasers is required for the treatment. At 8 months, the investigators reported improvement in skin texture and skin elasticity, as demonstrated in the images below, as well as rhytid reduction compared with baseline. Most adverse events were limited to mild, brief erythema.
Other nonablative lasers, such as the pulsed-dye laser, have been shown to improve dermal collagen. Histopathologic examination of scars treated with a 585-nm pulsed-dye laser revealed improvement in dermal collagen. The number of regional mast cells is increased in scars treated with pulsed-dye lasers. Because mast cells elaborate a variety of cytokines, their presence following irradiation and accompanying tissue revascularization may provide an explanation for therapeutic improvement following laser treatment. Using this concept, Zelickson et al  evaluated the use of a pulsed-dye laser in the treatment of rhytides. In a small pilot study, the authors noted improvement. However, the study results were tempered by the cosmetically unacceptable purpura that is usually observed following treatment with this laser.
The key problem in assessing evaluations of nonablative resurfacing in the last 5 years has been understanding its ability to induce objective clinical improvement.
Investigators using nonablative lasers have noted that the induction of new collagen creations are not specific to a wavelength. That is, identical alterations of collagen can be histologically demonstrated using the Er:glass laser, Nd:YAG, and diode lasers. The primary effects appear to be thermal injury to the dermis, inducing collagen remodeling and formation instead of vascular injury. What may be occurring is dermal remodeling or toning in a parallel fashion to the healing response elicited by an injury that initiates collagen regeneration, turnover, and deposition. 
Histological alteration do not exactly mirror clinical enhancement of skin. Results vary, and studies even of the same lasers with similar (but almost always slightly different) settings and parameters report different results (ie, some with clinically significant change and some without objective alterations in the skin).
Studies have been performed on pulsed-dye, 585- to 595-nm lasers; Er:glass, 1540-nm lasers  ; Nd:YAG, 1320-nm lasers; diode, 1450-nm lasers; and intense pulsed-light, 560- to 640-nm lasers with a cutoff filter. 
It might be best understood that Nonablative laser treatments are likely not the most effective treatments for rhytid reduction. However, they seem to be effective and useful modalities for amelioration of scars and superficial dyschromias. Obviously, for minimal facial damage, they allow patients to pursue their regular activities and thus are useful and important treatment options. 
Wanner et al  found that fractional photothermolysis for the treatment of facial and nonfacial cutaneous photodamage using a 1550-nm Er-doped fiber laser is a useful nonablative laser treatment.
Orringer et al  reported from a randomized, controlled, split-face clinical trial that 1320-nm Nd:YAG laser therapy in effective for treating acne vulgaris.
de Angelis et al reported good results using the fractional nonablative erbium:glass laser for treatment of striae rubra and alba ranging in maturation age from 1-40 years. 
Nonablative procedures are ideal for the younger person who wishes to improve the quality, the tone, and the texture of his or her skin. It is a technique ideally suited for the individual with early photoaging, not for one with class III rhytides. Nonablative treatment is also a good modality for saucerized acne scars and as a maintenance procedure following other more aggressive ablative laser procedures. Also see Facial Analysis for Skin Resurfacing.
Nonablative techniques have mainly been used on facial skin; however, interest is increasing in the role of these techniques on the neck, the hands, and possibly other areas of the body.
The techniques, because of their nonablative nature, appear to be safe. However, the risk of scarring is always present, which is true for any cosmetic procedure.