When your body is fighting off an illness, experiencing dry, irritated eyes is a common side effect. This discomfort arises when the tear film, a delicate three-layered coating that protects the eye’s surface, becomes unstable or deficient. The tear film is a mixture of water, oil, and mucus that keeps the eye lubricated and clear. The systemic stress of being sick can disrupt this balance, leading to the familiar gritty, burning sensation of dry eyes. This disruption is a combination of physiological and pharmacological factors that occur while the body is attempting to recover.
Dehydration and Reduced Tear Production
The most immediate physiological reason for dry eyes during sickness is often systemic dehydration. When you are ill, especially with a fever, vomiting, or diarrhea, your body loses fluids rapidly, and you may not be drinking enough water to compensate. Since the body is composed of over 50% water, significant fluid loss forces the body to conserve water for functions such as maintaining blood pressure and organ function.
The watery layer of the tear film, known as the aqueous layer, is produced by the lacrimal glands and is composed mostly of water. When overall body fluid volume is reduced, the body effectively “rations” water and reduces the output of the aqueous layer of tears. This decrease in tear production means the eye’s surface lacks the necessary hydration and lubrication, which can lead to irritation and damage to the corneal surface. Dehydration also causes the remaining tears to become more concentrated, which further contributes to the irritation and breakdown of the ocular surface.
How Immune Response Affects Tear Film Quality
Beyond simple fluid loss, the body’s immune response itself can directly influence the health of the eye’s surface. When fighting a pathogen, the body releases inflammatory substances, such as cytokines, into the bloodstream and surrounding tissues. These molecules are part of the process that fights infection, and they can travel throughout the body, including to the eyes.
The presence of these inflammatory mediators can affect the delicate balance of the tear film and the function of the lacrimal glands. Inflammation can disrupt the function of the meibomian glands, which produce the oily outer layer of the tear film. If this oil layer is compromised, the watery tears evaporate much faster than normal, leading to evaporative dry eye, even if the initial tear production is adequate. This systemic inflammation creates a localized cycle where the instability of the tear film causes more irritation, which in turn leads to further inflammation.
Common Medications That Dry the Eyes
Many people reach for over-the-counter medications to manage cold and flu symptoms, but these treatments are a common cause of dry eyes. Antihistamines block the effects of histamine and reduce runny noses and sneezing by drying out mucous membranes throughout the body. This drying effect extends to the lacrimal glands, thereby decreasing the production of the watery tear component.
Decongestants, such as those containing pseudoephedrine or phenylephrine, also contribute to ocular dryness. These medications work by narrowing blood vessels in the nasal passages to reduce swelling and congestion. This same constricting action can reduce blood flow to the tear glands, which results in less tear production. First-generation antihistamines, like diphenhydramine, are well-known for their strong drying effects, which can significantly reduce tear volume.
Soothing Symptoms and When to Seek Help
Dry eyes caused by temporary illness often respond well to simple remedies. The most direct step is to rehydrate by consistently drinking water, which helps restore the body’s fluid volume and supports tear production. Using preservative-free artificial tears is another effective measure, as these drops supplement the natural tear film without introducing chemicals that can cause further irritation.
Adjusting your environment can also provide relief, such as using a humidifier, especially during the night, to add moisture to dry indoor air. Taking frequent breaks from screens is important, as people tend to blink less often while focusing on digital devices, which increases tear evaporation. While dry eye during a cold is usually temporary, consult a healthcare provider if the dryness persists long after the illness or is accompanied by severe symptoms like intense pain, significant vision changes, or the feeling of something permanently lodged in the eye.