However, while the exact reasons remain somewhat elusive, doctors have developed several credible theories to explain this tearful side effect of yawning. To understand these speculations, we first need to delve into the basic composition and function of our tears.
The Science of Tears: More Than Just Water
Tears are not simply water; they are a complex fluid designed to keep our eyes healthy and comfortable. They are composed of three distinct layers that work in harmony to moisturize and protect the surface of your eyes. Understanding these layers is key to understanding why yawning can lead to tearing.
The Three Layers of Tears
According to the National Eye Institute (NEI), your tear film is made up of:
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Oily Layer: This outer layer, produced by Meibomian glands located under your eyelids, is composed of fatty oils. Its primary role is to prevent the watery layer from evaporating too quickly, ensuring long-lasting moisture for your eyes.
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Watery Layer: The middle and thickest layer is produced by the lacrimal glands situated under your eyebrows. This layer consists of water and water-soluble proteins. It nourishes the cornea, the clear front surface of the eye, and the conjunctiva, the membrane lining part of your eye and inner eyelids.
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Mucous Layer: This innermost layer is closest to the eye’s surface and is made of mucus. It helps the watery layer spread evenly across the eye, ensuring consistent moisture and lubrication.
This intricate tear film is spread across your eyes every time you blink, keeping them lubricated and clear. Tears also serve to flush out irritants and protect against infections. When your eyes “tear up,” it’s typically the watery layer that is being overproduced, explains Dr. Zeba A. Syed, a cornea surgeon at Wills Eye Hospital.
Yawning and Tearing: The Connection Explained
The most likely explanation for why yawning causes tearing eyes lies in the physical actions your face undergoes during a yawn. Think about it: when you yawn, your mouth opens wide, and your facial muscles contort. Often, you’ll close your eyes tightly or squint intensely. This facial contortion is the key to understanding the tearful reaction.
Facial Muscles and Tear Gland Pressure
As Vivian Shibayama, O.D., an optometrist with UCLA Health, explains, the scrunching of your face during a yawn puts pressure on the lacrimal glands, which are located right under your eyebrows. This pressure can stimulate these glands to produce more of the watery component of your tears. Essentially, yawning can be a bit like squeezing a water bottle – pressure leads to increased output.
Tear Duct Obstruction
Another contributing factor is related to your tear drainage system. Normally, tears drain away from your eyes through small ducts located in the inner corners of your eyes, as the NEI notes. However, the muscle contractions during a yawn can temporarily constrict or even close off these tear ducts. Dr. Massaro-Giordano describes this as “All that extra fluid has no place to go.” With the drainage system temporarily blocked and tear production potentially increased, the excess tears have no option but to overflow, leading to watery eyes. Once you finish yawning and your facial muscles relax, the tear ducts open again, and the excess tears drain away with your next blinks.
Why Doesn’t It Happen to Everyone, Every Time?
Interestingly, not everyone experiences watery eyes every time they yawn. Even if you are prone to tearing up when you yawn, it might not happen consistently. The frequency of this phenomenon can depend on individual anatomical variations. For example, Dr. Massaro-Giordano suggests that people with larger tear ducts might be more efficient at draining excess tears even during a yawn. In these cases, the increased tear production might be effectively managed by the drainage system, preventing the eyes from watering noticeably.
In conclusion, while the precise neurological pathways linking yawning and tearing remain an area of ongoing research, the current understanding points to a mechanical explanation. The physical act of yawning, with its associated facial contortions, places pressure on the tear glands and can temporarily obstruct tear drainage, leading to the common experience of watery eyes. It’s a fascinating example of how seemingly simple bodily actions can have complex and sometimes tearful consequences.
