When unwell, eyes often appear red or “bloodshot” due to prominent blood vessels. While usually temporary and harmless, understanding the underlying reasons can provide clarity.
The Science Behind Redness
The conjunctiva, a clear membrane covering the eye and lining the eyelids, contains tiny blood vessels. When irritated, inflamed, or infected, these vessels widen, or dilate, becoming more visible and causing the characteristic red appearance.
This response is part of your body’s immune defense. When sick, your immune system activates, leading to widespread inflammation that can extend to the eyes. This causes blood vessels in the conjunctiva to swell and increase blood flow, bringing immune cells to combat invaders or irritation, resulting in redness.
Common Illnesses and Their Eye Impact
Common illnesses contribute to bloodshot eyes. Viral infections like colds or flu cause general inflammation. Associated symptoms like coughing, sneezing, and nasal congestion can increase pressure around the eyes, leading to temporary vessel dilation and redness. Viral conjunctivitis, a common type of pink eye, often accompanies cold symptoms, directly inflaming the eye’s surface.
Allergies can mimic sickness symptoms and cause eye redness. When exposed to allergens like pollen or dust mites, your immune system releases histamines. These chemicals cause blood vessels in the conjunctiva to dilate and leak, resulting in itchy, watery, and red eyes. This inflammatory response attempts to flush out the perceived threat.
Conjunctivitis, or pink eye, is an inflammation of the conjunctiva and a frequent cause of red eyes. It can be triggered by viruses, bacteria, or allergens. In infectious forms, inflammation causes blood vessels to enlarge, making the eye appear red or pink, often with discharge or a gritty sensation. Bacterial conjunctivitis may present with pus, while viral forms typically produce watery discharge.
Sinus infections can also indirectly lead to bloodshot eyes. When sinuses become inflamed and congested, pressure builds behind the eyes. This localized pressure and inflammation affect surrounding tissues, contributing to redness and discomfort. The close proximity of sinuses to eye sockets means inflammation in one area can impact the other.
Contributing Factors During Illness
Several factors common during illness can exacerbate or cause bloodshot eyes. Dehydration, frequent when sick due to fever or reduced fluid intake, impacts eye moisture. Lack of water reduces tear production, essential for lubricating the eye’s surface. This dryness can lead to irritation, a gritty sensation, and visible redness.
Lack of sleep, common when unwell, also contributes to bloodshot eyes. Eyes need rest to replenish and repair. Insufficient sleep decreases oxygen to the eyes, causing blood vessels to dilate and appear red. Fatigue can also reduce tear production, leading to dry, irritated eyes prone to redness.
Frequent eye rubbing, a natural reaction to irritation during sickness or allergies, can worsen eye redness. Rubbing can cause tiny blood vessels to break, leading to a bloodshot appearance. It can also introduce germs, potentially worsening infections like conjunctivitis. Additionally, rubbing can release more histamines if allergies are present, intensifying itching and redness.
Fever, an elevated body temperature, can also cause eye redness. During a fever, the body’s overall inflammatory response is heightened. This systemic inflammation can cause blood vessels throughout the body, including those in the eyes, to dilate, which can lead to redness and discomfort.
When to Seek Medical Advice
While bloodshot eyes are often temporary, certain signs indicate a need for medical evaluation. Seek professional medical advice for severe, sudden eye pain. Changes in vision like blurriness, light sensitivity, or seeing halos, or thick, pus-like discharge, warrant prompt attention.
Other concerning symptoms include redness that worsens or does not improve after a few days, or if it affects only one eye. Extreme sensitivity to light (photophobia) or a persistent sensation that something is in your eye also warrant consultation. These symptoms, especially with headache, fever, nausea, or vomiting, suggest a more serious underlying condition requiring diagnosis and treatment.