Tears are produced to keep the eyes lubricated, nourished, and protected, forming a smooth, clear layer over the cornea. While tears are typically soothing, they sometimes sting or burn upon contact with the eye’s surface. This stinging sensation signals that the tear film’s balance is temporarily off or that the delicate surface of the eye is compromised.
The Chemical Composition That Causes Stinging
The sensation of stinging is frequently linked to an imbalance in the tear film’s chemical makeup. When the eye is irritated or dry, it triggers a rush of reflex tears. These tears are often produced too quickly to maintain their ideal chemical balance.
The primary mechanism for stinging is tear hyperosmolarity, which refers to an elevated salt concentration in the tear film. Normal tear fluid maintains a specific salt-to-water balance. When the watery part of the tear film evaporates too quickly, the remaining fluid becomes saltier. This hyperosmolar fluid is chemically irritating to the sensitive surface cells of the cornea, stimulating nerve endings and causing the stinging sensation.
Tear pH also plays a role, though less frequently than osmolarity. The normal pH of tears is near neutral, typically ranging between 7.0 and 7.6. A slight shift outside of this range, such as becoming mildly more acidic or alkaline, can contribute to irritation and a stinging feeling. However, the eye has robust buffering systems to stabilize pH, making hyperosmolarity the more common cause of irritation.
Environmental Factors and Eye Surface Dryness
Sometimes the tear fluid itself is normal, but the eye’s surface is too dry or damaged, leading to a stinging response. Extended screen use is a factor because focusing intensely causes the blink rate to drop by as much as 50%. Reduced blinking means the tear film is not spread evenly across the eye, causing it to break up and evaporate rapidly.
Low humidity, strong wind, or air conditioning can accelerate tear evaporation, destabilizing the protective tear film. When the tear film breaks down, the cornea is directly exposed to air, leading to dryness and irritation. This constant exposure can cause minor damage to the surface cells, known as micro-abrasions, which makes the eye surface hypersensitive even to a normal tear film.
In some instances, the mechanical friction of a dry eyelid moving over an unprotected cornea can lead to recurrent corneal erosion. Even normal tears hitting this compromised, sensitive surface can feel painful and trigger excessive, stinging tearing. External irritants like dust, smoke, or air pollution can also disrupt the tear film’s outer layer, triggering a stinging reflex.
Stinging Caused by Specific Eye Conditions
Chronic inflammatory conditions of the eye can alter the local environment, leading to persistent stinging. Blepharitis, which is inflammation of the eyelids, often results from clogged oil glands or bacterial overgrowth at the base of the eyelashes. These blocked meibomian glands fail to secrete the necessary oil layer that prevents tear evaporation.
The resulting poor-quality tear film causes the tears to evaporate quickly, leading to evaporative dry eye and hyperosmolarity, which results in stinging. Allergic conjunctivitis causes stinging through a different mechanism involving the immune system. When the eye encounters an allergen, specialized cells release inflammatory chemicals like histamine.
This histamine binds to receptors on nerve endings in the eye, causing inflammation and triggering the sensation of burning, itching, and excessive tearing. Infectious conjunctivitis, commonly known as pink eye, causes stinging and a gritty sensation due to the direct inflammation of the conjunctiva. The infection causes a surge of inflammatory molecules that irritate the cornea and trigger a watery reflex.
Practical Steps for Relief and Treatment
Immediate relief from stinging tears can often be achieved by addressing the underlying dryness or irritation. Lubricating eye drops, often referred to as artificial tears, are a primary defense that helps restore the balance of the tear film. For individuals who need to use drops frequently, preservative-free formulations are recommended to avoid irritation from chemical preservatives.
If the stinging is related to digital eye strain, consciously adhering to the 20-20-20 rule can help: look 20 feet away for 20 seconds every 20 minutes to encourage a full blink. Using a humidifier, particularly in dry environments, can also help slow the evaporation of tears. Warm compresses applied to the eyelids can soothe irritation, especially when blepharitis is suspected.
It is important to seek professional medical attention if the stinging is accompanied by specific warning signs. These include a sudden, painful change in vision, the presence of a thick, greenish, or pus-like discharge, or extreme sensitivity to light. Any symptom that persists for more than a few days, despite using over-the-counter drops, warrants an examination by an eye care specialist.