The World Health Organization (WHO) described oral lichen planus (OLP) as “a chronic inflammatory disorder of unknown etiology with characteristic relapses and remissions, displaying white reticular lesions, accompanied or not by atrophic, erosive and ulcerative and/or plaque-type areas. Lesions are frequently bilaterally symmetrical. Desquamative gingivitis may be a feature” [1]. Although its etiology is unknown, it is believed to be autoimmune in nature by observing an imbalance of the immune system mediated by auto-cytotoxic CD8+ T lymphocytes that trigger apoptosis of oral epithelial cells, generating the inflammatory lesion [2]. There are psychological factors such as anxiety, depression and stress that predispose to the manifestation or recurrence of OLP lesions [3,4,5]. The average prevalence of OLP worldwide is 1.27%, with an oscillation between 0.1 and 4% due to geographic and pathogenic factors [6]. It mainly affects women starting from the age of 40, although it has also been seen in children [7]. Histologically, it is characterized by hydropic degeneration or liquefaction of the basal epithelium with the presence of Civatte bodies (apoptotic keratinocytes) and a subepithelial inflammation with a lymphocyte infiltrate, mainly CD8+ T cells in a band shape [8]. These histological findings, according to the WHO, are used for a definitive diagnosis of OLP [8]. OLP lesions are considered an oral potentially malignant disorder (OPMD), defined as “clinical manifestations that carry a risk of developing cancer in the oral cavity, either in a clinically definable precursor lesion or in a clinically normal mucosa” [9]. OLP may have a variable risk of malignant transformation to oral squamous cell carcinoma, from 0.44 to 2.28%, as reported in recent systematic reviews and meta-analyses [10]. The risk factors for malignant transformation are smoking or chewing tobacco [11], presenting the erosive form of OLP, more specifically with ulcerative and/or erosive lesions on the edges [12], advanced age, alcohol consumption, presence of the OLP lesion on the tongue [10], and/or presence of HBV (hepatitis B virus) or HCV (hepatitis C virus) infections [7]. The evolution of OLP is heterogeneous; therefore, patients should be monitored through periodic follow-ups even in the absence of symptoms, in order to identify worrying signs of malignant transformation [13]. White lichen lesions (reticular or plaque-shaped forms) mostly heal spontaneously, while red lesions (atrophic–erosive) need treatment [14]. Among the different treatment modalities is the administration of retinoids, immunosuppressive drugs, antifungal agents, surgery and laser, most of which are aimed at relieving signs and symptoms, as well as at preventing possible recurrences [15]. Even so, it is advisable to have a healthy lifestyle with good oral hygiene, exercise and sufficient rest and relaxation in order to achieve control of OLP outbreaks [16]. Normally, corticosteroid therapy is the first choice; however, side effects such as insomnia, mood swings, fatigue, fluid retention, nausea, dry mouth, sore throat, thinning of the oral mucosa and yeast overgrowth may appear [15]. Regarding the most used topical corticosteroids for the treatment of lichen planus, triamcinolone acetonide formulated at 0.3–0.5% is used, followed by fluocinolone acetonide at 0.05% and finally propionate of clobetasol at a concentration of 0.025–0.05% [14,17]. Another treatment option is photobiomodulation (PBM), in which a laser or a non-ionizing radiation (LED) (at 400–1.100 nm wavelenght) is used to beneficially influence cell metabolism, without harm to the cells or to the basal temperature of the body [18]. Different types of laser light such as ultraviolet, diode and helium–neon are used, as well as different output powers, irradiation times, doses and number of sessions for each OLP lesion [19,20]. Although there is no standardized protocol, Del Vecchio et al. [18], in 2021, defined a dose oscillating between 2 and 3 J/cm2 as effective in OLP treatment to obtain the desired biological effects [21]. Diodes are often used in dentistry and serve as a preventive treatment for oral mucositis caused by chemotherapy and radiotherapy applied in cancer treatment [22] and to reduce the symptoms of OPMDs [21], as in the case of OLP. This is due to their beneficial effects at the cellular level, such as on proliferation at lower doses of energy and apoptosis at higher doses of energy [23], and at the systemic level, with an analgesic action. PBM was shown to reduce pain and promote clinical improvement of OLP lesions [24], with a decrease in size and erythema, using wavelengths between 630 and 980 nm with an output power of 20 to 300 mW and an exposure time of 10 s to 15 min [25]. These beneficial effects of PBM on OLP would be explained by its ability to delay cell differentiation, improve healing and re-epithelialization, reduce inflammation through immunomodulation and exert an analgesic effect (through the production of beta-endorphins and enkephalins and the reduction of histamine and bradykinin, in addition to the reduction of the activity of sensitive C fibers) [18]. Although more studies are needed and sometimes there are contradictory results, the latest research suggests that PBM could be just as effective as topical corticosteroids, but without their adverse effects, which makes it a very promising therapy [26]. The aim of this systematic review w2as to provide a synthesis of the scientific evidence of PBM usefulness in oral medicine and its contribution to improving the quality of life of patients. It focuses on–atrophic– erosive lichen planus since this is the OLP form that reduces the most the quality of life of patients and is considered at the greatest risk for malignant transformation. The purpose of this systematic review was to determine the effects of PBM on the atrophic–erosive form of OLP by in relation to the physical parameters of the laser, the stimulation of healing, the improvement of painful symptoms and the anti-inflammatory effects, comparing its effectiveness with other treatments, such as corticosteroids. Our hypothesis was that PBM could be an effective therapeutic alternative to conventional treatments.