Stimulus conditions eliciting sneezing in response to bright light

The photic sneeze reflex (PSR) is an involuntary sneezing response to bright light exposure, affecting approximately 25% of the population. Despite its long history in scientific literature, the underlying mechanisms remain unclear. Several theories, including optic-trigeminal summation, parasympathetic hypersensitivity, and parasympathetic generalization, have been proposed, but none have been conclusively validated. Reproducing the PSR reliably in a laboratory setting is crucial for understanding its neural underpinnings, yet the specific light parameters that trigger PSR are not well-defined. This mini-review aims to consolidate current knowledge on the light stimulus parameters (intensity, spectral composition, wavelength, duration, timing, spatial configuration) that elicit the PSR. A comprehensive literature search was conducted using MEDLINE (PubMed), Google Scholar, Google Books, and Google, employing terms related to photic sneezing in multiple languages. Articles from 2020 to 2024 were screened, resulting in 167 records, with seven studies focusing on stimulus parameters included in this review. The reviewed studies, including four case reports and three laboratory experiments, consistently support that bright light can induce sneezing in susceptible individuals. However, there is significant variability in the methodologies and outcomes, limiting comparability and indicating a need for systematic investigation. No study has yet examined the parametric relationship between light parameters and the PSR. The heterogeneity of methods and findings in the existing literature highlights the lack of standardized research on the specific light parameters that trigger the PSR. This review underscores the need for controlled experiments to clarify these relationships and improve our understanding of the underlying neural mechanisms. Existing research on photic sneezing stimulus parameters is fragmented and lacks systematic approaches. Future studies should focus on standardized, parametric investigations to elucidate the light-sensitive mechanisms of the PSR.