Why Do Your Eyes Water When You Yawn?
Your eyes can water when you yawn because yawning can activate reflex tearing while the muscles around your eyes and eyelids contract. Published research on lacrimation describes yawning as one of the non-emotional triggers capable of stimulating the tear-producing pathway, which involves sensory signals, parasympathetic nerves, and the lacrimal glands. Under normal conditions, basal tear production is about 2 microliters per minute, but reflex stimulation can temporarily increase secretion enough for tears to accumulate on the eye's surface. Blinking normally moves this fluid toward two drainage openings in each eye, one in the upper eyelid and one in the lower, but the prolonged eye squeezing and facial movement that accompany a yawn can briefly alter the usual balance between tear production and drainage. The extra fluid can then spill over the eyelid, which is why a deep yawn sometimes leaves your eyes looking as though you've been crying even though no emotional tears are involved.
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