The most frequent adverse effect in skin from nonablative laser treatment is erythema [ 108-111]. Erythema may be accompanied by edema, and is a reflection of the inflammatory response. Even when the clinician or operator uses careful precautions, erythema may be observed. In fact, the presence of perifollicular erythema or edema (inflammation surrounding the hair pore) is used by some clinicians as an indication of effective treatment. Despite the high frequency, these events are reversible, and largely considered to be of no human health concern.
In the treatment of facial telangiectasisa, that is, spider veins, using a diode-pumped Nd:YAG laser, all subjects reported erythema [112]. Similarly, in another study using ruby laser to treat facial telangiectasisa, all subjects experienced erythema [113]. In a study by Wheeland [23], 33% of the subjects experienced erythema rated as minimal using a portable diode laser for hair removal. Facial resurfacing using a Nd:YAG as reported by McDaniel [114] found erythema that lasted up to five days in this aggressive treatment. Finally, using a 1450 nm diode laser as a treatment for facial acne, it was found that the side effects of erythema and edema were minimal and transient [115]. In all these examples, erythema was observed, but it was minimal to moderate and perhaps, more important, reversible.
In general, erythema resulting from laser treatment is diffuse within the treatment area. There is, however, a report of reticulated erythema in subjects following repeated laser treatment [116]. In these ten cases, subjects received high fluence (i. e., >40 J/cm2) diode laser and after one to five treatments the reticulated erythema was noted. Whereas the authors state that the prognosis is excellent once treatment is stopped, repeated exposures may result in pigmentary changes.