Yawning often leads to watery eyes, a common experience that prompts questions about its biological causes. Understanding why eyes water during a yawn involves exploring the body’s tear production system and the specific physical actions that occur when we yawn.
The Anatomy of Tear Production
Tears are produced by the lacrimal apparatus, which includes the lacrimal glands and a network of drainage ducts. The main lacrimal glands, located in the upper outer corner of each eye, are responsible for secreting the watery component of tears. These glands continuously produce lacrimal fluid, which is primarily composed of water and salt, and is spread across the eye’s surface with each blink.
Tears serve several protective and lubricating functions for the eyes. They help keep the conjunctiva and cornea moist, provide essential nutrients, and flush away foreign particles, dust, or irritants that may enter the eye. After lubricating the eye, tears collect in a triangular space near the inner corner of the eye, called the lacrimal lake. From there, they drain through tiny openings called lacrimal puncta, flow into lacrimal sacs, and then pass through the nasolacrimal ducts (often referred to as tear ducts) into the nasal cavity. This drainage system ensures a constant turnover of tears, maintaining ocular health.
The Mechanics of a Yawn
Yawning is a complex, involuntary reflex involving a series of coordinated muscle movements. It begins with a deep, prolonged inhalation, typically through both the nose and mouth. During this phase, the diaphragm and intercostal muscles in the ribs contract, drawing a significant amount of air into the lungs.
Simultaneously, the jaw opens widely, and various muscles in the face, neck, and throat engage. Muscles around the mouth and eyes stretch and tense, leading to the characteristic wide gape and sometimes a facial grimace. This muscular action causes the airway, including the throat, to dilate considerably, expanding to several times its normal size. After this intense stretching and inhalation, muscles relax as air is exhaled.
Why Yawning Makes Your Eyes Water
The watery eyes experienced during a yawn are primarily a mechanical consequence of these powerful muscle contractions. As the facial muscles around the eyes tighten and stretch during a yawn, they exert pressure on the nearby lacrimal glands. This pressure can temporarily stimulate the lacrimal glands, causing them to release a small amount of tear fluid.
In addition to stimulating tear production, the muscular action can also mechanically squeeze existing tears from the lacrimal glands or tear ducts. This effect is similar to “wringing out” a sponge, where the pressure forces the fluid to exit. The movement and pressure can also momentarily disrupt the normal drainage of tears through the nasolacrimal ducts, leading to a temporary pooling of tears on the eye’s surface before they can drain away.