Increased Er:YAG pulse duration is associated with an increased risk of pigment  changes, potentially because a longer pulse duration deposits more energy per  pulse and thereby causes more thermal damage to surrounding tissue. The use  of a fractionated beam delivery system decreases the risk of pigmentary  changes. Pigmentary changes often fade with time; hyperpigmentation is more  common than hypopigmentation and more likely to resolve. For persistent  hyperpigmentation, 4% topical hydroquinone will help lighten the skin. For  hypopigmentation, which is thought to result from inflammation that compromises  melanocyte function, topical steroids may be helpful. Other options include sun  exposure, blue laser therapy, intense pulsed light, and fractionated CO2 laser  treatments

For many years, carbon dioxide (CO2) lasers (wavelength 10,600 nm) were the  only lasers available for laser skin rejuvenation; nowadays, there are many more options, including the solid-state erbium-doped yttrium aluminum garnet Er:YAG  (2,940 nm), diode (810 and 940 nm), and erbium:glass lasers (1,540 and 1,550  nm). 

1996 short-pulse Er:YAG lasers were approved, with pulse lengths of 250-350  µs; however, variable and longer-pulse Er:YAG lasers with pulse widths of 500 µs  to 10 ms were subsequently approved in 1999  

Er:YAG is absorbed by water in the epidermis and papillary dermis, resulting in  two effects that promote skin rejuvenation. The first is vaporization of the  epidermis, which requires the dermal appendages (hair follicles and sweat  glands) to resurface the skin in order to heal. Secondly, thermal injury in the  dermis stimulates collagen production, which improves the appearance of photo  damaged skin while reducing visible rhytids and scars.  

Laser skin rejuvenation treatments are generally classified into two  categories, ablative and non-ablative. Ablative lasers vaporize and/or coagulate  the most superficial layers of skin, which results in rejuvenation via re epithelialization and collagen stimulation. The classic example of an ablative  laser used for skin rejuvenation is the CO2 laser. Non-ablative laser treatments  do not remove the epidermis but nonetheless cause controlled thermal injury,  which stimulates the production of collagen and elastin. Examples include the  diode, erbium:glass, and neodymium:YAG (Nd:YAG 1,320 nm) lasers. While  ablative treatments typically provide more dramatic results, non-ablative lasers  are preferred by many patients because of their lower risk profile and decreased  post-treatment recovery time. However, more treatments with non-ablative lasers  are often required to achieve the same effect as a single treatment with an  ablative laser. The Er:YAG laser is considered an ablative laser.

Ablative laser energy delivery is commonly performed in one of two ways: with  full-field therapy or via a fractionated beam. While a full-field approach treats the  entire area of interest, fractionated treatments ablate microscopic vertical  columns within the treatment area while leaving intervening areas that remain  unaffected. This approach leaves uninjured skin and dermal appendages, which  promote re-epithelialization, reduce adverse side effects, and stimulate collagen  production.  

In either case, the goal is to ablate down to the papillary dermis, which will  maximize collagen stimulation and tissue tightening while minimizing scarring.  The depth at which the papillary dermis is found varies throughout the face, with  the eyelids being the thinnest at about 150 µm and the chin being thickest at  approximately 200 µm. Likewise, the thickness of the dermis varies from about  200 µm in the eyelids to approximately 1300 µm in the chin. The neck is the 

thinnest, with an epidermal thickness of roughly 100 µm and a dermal thickness  of approximately 150 µm.