Dry eye disease happens when your tears can’t adequately protect and lubricate the surface of your eye. This can mean your eyes don’t produce enough tears, or the tears evaporate too quickly because their chemical composition is off. With a global prevalence around 35%, it’s one of the most common eye conditions, and it rarely has a single cause. Most cases involve a combination of factors working together.
How Your Tear Film Works
Your tear film is only about 3 micrometers thick, but it has a surprisingly complex structure. It functions as a semi-viscous gel made up of three overlapping layers: an inner mucin layer that helps tears stick to the eye’s surface, a middle watery layer that delivers oxygen and nutrients to the cornea, and an outer lipid (oil) layer just 40 to 160 nanometers thick that acts as a barrier against evaporation.
When any of these layers is disrupted, the tear film becomes unstable. It breaks apart too quickly, leaving patches of the cornea exposed. Clinicians measure this with a tear break-up time test: if the tear film falls apart in under 10 seconds, it’s considered abnormal. Once the film destabilizes, the remaining tears become saltier (hyperosmolar), which irritates the eye’s surface and triggers inflammation, creating a cycle that makes the problem worse over time.
Evaporative Dry Eye and Oil Gland Problems
The most common form of dry eye is evaporative, meaning tears disappear from the surface too fast. This type, either alone or combined with low tear production, accounts for up to 85% of all cases. The usual culprit is dysfunction of the meibomian glands, tiny oil-producing glands along the edges of your eyelids.
Healthy meibomian glands secrete a thin oil that spreads across the tear film and slows evaporation. When these glands malfunction, they produce either too little oil or oil of poor quality. The underlying problem is a buildup of thickened skin cells inside the gland ducts, which blocks them. Over time, the backed-up oil causes the ducts to swell, and eventually the glands shrink and stop working altogether. Without that protective oil layer, tears evaporate rapidly, and the eye dries out between blinks.
Low Tear Production
The other major category is aqueous-deficient dry eye, where the lacrimal glands (the tear-producing glands above each eye) simply don’t make enough fluid. Inflammation plays a central role here. When the lacrimal gland becomes inflamed, it produces fewer tears, and the resulting dryness drives even more inflammation.
Autoimmune conditions are the most well-known cause. In Sjögren’s syndrome, the immune system attacks moisture-producing glands throughout the body, including the lacrimal and salivary glands. Other autoimmune diseases like rheumatoid arthritis and lupus can have similar effects. In severe cases, chronic inflammation can scar the lacrimal gland so extensively that it loses its ability to recover.
Hormonal Changes
Hormones, particularly androgens, have a direct effect on meibomian gland function. Androgens help regulate how much oil the glands produce and what that oil is made of. When androgen levels drop, the composition of meibomian oil shifts: levels of the lighter, more fluid fats decrease while cholesterol increases. Higher cholesterol content raises the oil’s melting point and makes it thicker, causing it to stagnate and plug the glands rather than flowing smoothly onto the tear film.
This explains why dry eye becomes more common during menopause, with aging in both sexes, and in people with Sjögren’s syndrome. The common thread in all three situations is androgen deficiency. Patients taking anti-androgen medications (sometimes prescribed for prostate conditions or hormone-sensitive cancers) show a measurable decrease in the quality of their meibomian gland secretions, confirming the hormonal link.
Medications That Dry Your Eyes
An estimated 62% of dry eye cases in older adults can be traced to systemic medications. The list is long: antihistamines, antidepressants, diuretics, blood pressure medications, anti-anxiety drugs, NSAIDs like ibuprofen, and many others. Many of these drugs share a common mechanism. They have anticholinergic activity, meaning they interfere with a class of cell-surface proteins that play a key role in stimulating tear, mucus, and oil secretion.
Some medications cause problems through a different route entirely. Drugs like amiodarone, aspirin, ibuprofen, and certain antimalarials can be secreted into the tear film itself, where they form tiny crystals that irritate the eye’s surface. Medicated eye drops, especially those used for glaucoma, can also worsen dry eye. Most glaucoma drops contain a preservative called benzalkonium chloride, a known cell toxin that causes surface inflammation with long-term use.
Screen Time and Blinking
You normally blink about 15 times per minute. When staring at a screen or reading, that rate can drop by half. Each blink spreads a fresh layer of tears across the cornea and stimulates the meibomian glands to release oil. Fewer blinks means the tear film sits exposed longer between refreshes, giving it more time to evaporate and thin out. This is why many people notice dry eye symptoms worsen during the workday and improve on weekends or vacations, particularly if their job involves extended computer use.
Environmental Triggers
Low humidity is one of the strongest environmental risk factors. Dry air, whether from air conditioning, forced-air heating, airplane cabins, or arid climates, pulls moisture from the tear film faster than the eye can replace it. Temperature extremes also affect the ocular surface, both directly and by changing indoor humidity levels. High altitude, where the air is thinner and drier, has a similar effect. Wind accelerates evaporation even further, which is why dry eye symptoms often flare on windy days or when cycling without eye protection.
Surgery and Nerve Damage
Refractive surgeries like LASIK are a well-recognized cause of dry eye. During the procedure, creating the corneal flap severs tiny nerves in the cornea. These nerves are critical to the entire tear system: they trigger the blink reflex, stimulate tear secretion, help maintain tear film stability, and support the healing and barrier function of the corneal surface. When the nerve feedback loop is disrupted, the eye essentially loses its ability to sense dryness and respond by producing tears. For most people, the nerves regenerate over several months, but some experience persistent dry eye symptoms that last a year or longer.
Age and Sex
Dry eye becomes more common with age, affecting about 37% of people over 40 compared to 35% of those 40 and under. The difference is driven by a combination of the factors above: declining hormone levels, accumulated meibomian gland damage, increased medication use, and age-related decreases in lacrimal gland output. Women are affected more often than men at every age, largely because of hormonal shifts during menopause and the sharper decline in androgens that accompanies it.
In practice, most people with dry eye disease don’t have a single isolated cause. A postmenopausal woman taking an antihistamine and working at a computer in an air-conditioned office has at least four contributing factors at once. Understanding which ones apply to you is the first step toward finding a management approach that actually helps.