When we cry, our eyes turn red because tears contain enzymes and proteins that can irritate the eyes and cause inflammation of blood vessels, which gives this red color to the eyes.
Tears are produced by the tear glands, located under the upper eyelid. These glands secrete a liquid primarily composed of water, but also of mineral salts, proteins, and enzymes such as lysozyme. With each blink, the eyelid spreads this liquid to form a thin protective layer on the surface of the eye. This serves to hydrate, clean, and protect our eyes from microbes and other impurities. When we experience a strong emotion, our brain sends nerve signals that instruct the tear glands to increase their production. As a result, they release an excess of liquid that overflows in the form of tears.
When we cry for a long time, our body reacts by increasing blood circulation directly around the eyes. In simple terms, the small blood vessels on the surface of the eye and on the conjunctiva (the transparent membrane that covers the eye) will dilate and fill with more blood. As a result, the eyes become visibly red because these dilated vessels become more visible through the thin transparent layer of the ocular surface. This reaction is due to the autonomic nervous system (which unconsciously manages many functions of our body). With continued rubbing or drying of the eyes, this phenomenon can become even more pronounced, pushing even more blood to the surface and significantly increasing the sensation of discomfort and visible redness.
When we cry, tears contain a good amount of salt. This salt, when it remains on the surface of the eye for too long, can disturb its natural protective film. As a result, the eye becomes more easily irritated. Furthermore, by mechanically rubbing the eyes while crying, we risk exacerbating this irritation, which stimulates inflammatory reactions that cause the famous redness. In other words, it’s as if the eyes are defending themselves from a temporary aggression: they react by becoming all red, sensitive, and slightly swollen.
When you cry, your eyes can interpret certain substances in tears as mild irritants. Your immune system reacts by raising the alarm: cells called mast cells then release histamine. This histamine quickly causes blood vessels in the eye to dilate. The result: your eyes turn red and become swollen. This reaction is normal, but obviously uncomfortable if you're trying to hide that you've been crying!
The redness of the eyes after crying varies from person to person, depending on their individual sensitivity. Each person has a different ocular reactivity: some experience pronounced redness after just a few tears, while others may cry for a long time with little visible trace. This difference depends on factors such as the thickness of the skin around the eyes, the ease with which blood vessels dilate, and genetic predisposition. Those with sensitive eyes or very thin skin often show redness more easily and quickly than others. Similarly, individuals suffering from seasonal allergies or inflammatory conditions like rosacea are more prone to marked irritation as soon as they shed a few tears.
The phenomenon of "red eyes" after crying occurs partly because your blood vessels dilate significantly due to the effects of emotion and the mechanical stimulation caused by rubbing the eyes.
Some studies suggest that after crying, our body naturally releases endorphins. This could explain why many people feel relieved after crying: it acts as a form of natural soothing.
Did you know that humans are the only species that cries to express specific emotions such as sadness or joy? In other animals, tears serve exclusively a protective and hydrating function.
There are three different types of tears: basal tears, which keep the eyes moist; reflex tears, triggered by irritants like onion smoke; and emotional tears, which we shed during stressful or moving situations.
Occasionally holding back tears is generally not harmful to eye health. However, crying plays a natural role in clearing away irritating particles and soothing the eye. Constant suppression of tears could contribute to the accumulation of emotional stress as well as prolonged eye irritation.
To quickly reduce eye redness after crying, you can apply a cold compress or use moisturizing drops to refresh and soothe your eyes. Be sure to blink regularly to restore natural lubrication.
Individual sensitivity plays a major role in eye redness after crying. Some people have more sensitive blood vessels or thinner skin around the eye area, making them more prone to visible reddening.
When you cry, the chemical composition of emotional tears differs from that of regular tears. These tears contain more proteins and other irritating substances that can cause a tingling or discomfort in the eyes after crying for a long time.
No: strong emotions are not the only reason why eyes become red. Other factors, such as allergies, eye fatigue, dryness, or exposure to external irritants, can also cause this symptom.
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