Unpacking the photic sneeze reflex (ACHOO): Prevalence, association with other traits and replication of recent findings
Around 1 in 5 people sneeze in response to exposure to bright light, a trait commonly referred to as the photic sneeze reflex or Autosomal Dominant Compelling Helio-Ophthalmic Outburst (ACHOO) . While a genetic basis of photic sneezing has been identified, pointing to specific single-nucleotide polymorphisms (SNPs), very little is known about the mechanisms underlying photic sneezing. As sneezing is a vector for pathogen transmission and can increase accident risk while conducting vehicles, understanding what underlies photic sneezing should be a key priority, in addition to understanding the underlying biology out of pure scientific interest.
We recently completed a series of surveys targeted towards photic sneezers to investigate whether the photic sneezing trait is related to other light-mediated functions. These light-mediated functions included photophobia, sleep and circadian rhythms (set by the light-dark cycle), how photic sneezing varies with the time of day, and which types of light (sunlight, bright indoor illumination, …) can cause photic sneezing. The surveys, which have had >2000 participants, have revealed a series of new aspects surrounding the photic sneeze reflex:
- Sneezing in response to light is not an all-or-nothing phenomenon but a very graded phenomenon. Some people sneeze upon light exposure, and others use light to further sneezes triggered by other causes (e.g. exposure to dust).
- Photic sneezing appears to correlate with sensitivity to light and visual discomfort.
- Photic sneezing does not appear to correlate with other traits we measured, including chronotype.
In addition, we performed a meta-analysis on the prevalence estimates of photic sneezing across >15 scientific articles on this topic, finding an aggregate prevalence of 0.21 [0.17-0.26 95% CI]. These estimates were generally based on phenotypes where people were asked a yes-no question whether they sneezed in response to light, thereby missing a lot of the graded information about photic sneezing highlighted above.
In our previous (unpaid and unfunded) surveys, we specifically recruited photic sneezers. Consequently, we are missing a lot of information from people who do not identify as photic sneezers. We would therefore like to replicate our findings in an independent sample, recruiting from a wide and diverse range of people, including those who do not self-select into the survey. Participants will complete a survey using previously defined and validated instruments. The study will be submitted as an amendment to an existing ethics approval at the University of Oxford (R64329).
The goal of the survey is to examine the following hypotheses, and confirm our findings in an independent sample:
- H1: Photic sneeze propensity is correlated with light sensitivity and visual discomfort (as measured using standard instruments).
- H2: The prevalence of people who identify as photic sneezers is around 17%-26%.
We will ask participants to complete a series of questions related to their sneezing, including rating the frequency of sneezing under a wide variety of lighting situations (direct sunlight, full daylight (not direct sun), overcast day, …) as well as upon exposure to other stimuli (inhaling cold air, inhaling dust, eating chocolate, …) using a five-point Likert scale (never, rarely, sometimes, very often, always). In addition, we will ask participants to complete a series of standardised instruments: the Visual Discomfort Scale (VDS), the Visual Light Sensitivity Questionnaire-8 (VLSQ-8) and the Photosensitivity Assessment Questionnaire (PAQ). Furthermore, we will ask participants if they identify as a “photic sneezer” and know the phenomenon.
Across the sample, we will also calculate the proportion of people identifying as photic sneezers. We will correlate (Spearman correlation) the VDS, VLSQ-8 and PAQ scores (both sub-scales) with the photic sneeze propensity score, constructed from the frequency that people report that they sneeze when entering bright light. As a further analysis, We will cross-correlate (Spearman correlation) the self-reported frequencies of sneezing in response to different stimuli (light and non-light). Further exploratory analyses will be done, and will be identified as such in the write-up of this work.
We will recruit a nationally representative sample of 1000 participants for a 40-minute study. At £5.00 per completed survey (£7.50 hourly rate), this corresponds to a total participant cost of £7,437.78. With the 33% service fee, the entire cost of the survey is £9,893.25.
The hypotheses above are pre-registered at AsPredicted.org (links to follow).
All materials (including custom questionnaire questions), data (including those from previous surveys), and code to analyse the data will be made available as part of a dedicated GitHub repository upon submission of the preprint of the work proposed here. The GitHub repository will also be archived using Zenodo.org and receive a DOI such that the repository is citable. Code to analyse the data will be subjected to the CODECHECK process (https://codecheck.org.uk/) to ensure the reproducibility of the analysis. Our group has extensive experience in engaging in open and transparent science, making available data sets (e.g., GitHub - spitschan/IlluminationSpectraDataset: Code for the paper "Variation of outdoor illumination as a function of solar elevation and light pollution" by Spitschan, Aguirre, Brainard & Sweeney (2016).), code (e.g., GitHub - spitschan/SilentSubstitutionToolbox: Toolbox to simulate colorimetric observers for evaluation of photoreceptor isolation), open-access platforms (e.g., https://luox.app/), and other outputs (e.g., https://enlightenyourclock.org/ for an open-access comic book) routinely, and pre-registering studies. In addition to submitting this work for eventual publication as an open-access article, we will also run a public talk presenting the findings of this study and the previous studies open to everyone.