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Background: Yawning is a stereotypical muscular activity observed in most vertebrates. The surrounding pharyngeal muscles undergo complete tension, leading to the dilation of the entire respiratory tract. Frequency of yawning is commonly associated with sleepiness and sleep deprivation with several different hypotheses on primary cause of yawning having been proposed in literature. Objective: A literature review was conducted to investigate the primary factors contributing to yawning. Materials and methods: In December 2023, an initial set of relevant articles was identified in the electronic database MEDLINE (PubMed) using the Medical Subject Headings (MeSH) for the search term ‘yawning’. In a second step a targeted manual search was conducted for several relevant topics in this research field. Results: Existing literature has demonstrated that “yawning” can be attributed to various factors. However, there is currently no consensus on the primary cause of yawning. While the reflex mechanism has been thoroughly investigated, there are no studies to date that could definitively establish the primary factors for yawning. Conclusion: Due to the heterogeneous and limited data, further studies are needed to examine the diverse hypotheses and the complex muscular mechanisms in both healthy subjects and patients with sleep disorders to address the gaps of knowledge.