Photobiomodulation (PBM), as a form of light therapy, has been applied broadly in the medical practice. The biological photoreceptors use small-molecule cofactors called chromophores to detect light and convert a physical signal into a biochemical signal transmission cascade. Visible light (380–780 nm) can activate specialized photoreceptors to stimulate vision and regulate circadian rhythm. Compared with visible light, near-infrared (NIR) light (780–1,100 nm) has better tissue penetration depths, enabling us to carry out non-invasive low-level laser therapy (LLLT) for different tissues. Mitochondrial cytochrome c oxidase is the main NIR photoreceptor. The basic effect is to promote the generation of ATP through the respiratory chain. LLLT can enhance blood circulation, alleviate inflammation, promote muscle damage repair, stem cell proliferation and so on. The neuroprotective effect of LLLT on central nervous system (CNS) diseases has been preliminarily verified in animal models, which is expected to improve the cognitive function of Alzheimer’s patients, motor symptoms of Parkinson’s patients and mental disorders of patients with depression, thus improving the quality of life of patients. Understanding its protective effect and mechanisms will contribute to better therapeutic application in the future. In this review, we will discuss the antidepressant effect of LLLT, its possible mechanisms, and existing problems with its applications.

On January 30, 2020, the World Health Organization (WHO) announced COVID-19 as the sixth public health emergency of international concern, and on March 11, 2020, the WHO declared that COVID-19 is a pandemic. To date, patients with COVID-19 are present in most countries in the world. Coronavirus disease 2019 (COVID-19) is caused by a coronavirus SARS-CoV-2. The COVID-19 virus and the 2003 severe acute respiratory syndrome (SARS) virus are approximately about 79% homologous, and their transmission modes are similar, but the transmission speed and range of COVID-19 virus far exceed those of the 2003 SARS virus, causing people to experience panic, anxiety, and depression. After the SARS epidemic, many survivors and medical workers had severe post-traumatic stress disorder (PTSD), which seriously affected their quality of life. Here, we reviewed the situations of PTSD after the SARS epidemic. The lessons and experiences of PTSD caused by SARS may help deal with the more severe occurrence of PTSD during and after the COVID-19 epidemic.