MadSci Network: General Biology

Re: why do we get swollen eyes after crying or sleeping?

Date: Tue Apr 3 06:36:21 2001
Posted By: Benoit A. Bacon, Post-doc/Fellow, Psychology, University of Glasgow
Area of science: General Biology
ID: 984739305.Gb

Dear Becky,

     Thank you for your interesting question or should I say interesting 
questions, since our eyes are swollen for different reasons after 
crying and after sleeping. 

     Why do we have swollen eyes after crying is the most interesting 
question. Tears are salty, watery secretions that keep two important 
parts of the eye constantly moist. They flow over the cornea, the 
transparent coating of the eye, and they lubricate the conjunctiva, the 
membrane covering the white of the eye and lining the inside of the 
eyelids. Tears also wash away stray bits of dust and grit and help 
keep your eyes free of infections. These tears that constantly keep 
your eyes moist, called the basic tear secretions, are produced on 
the conjunctiva and also in the eyelids. These, of course, do not 
cause swollen eyes.
     The tears that we cry over failed exams, lost loves or bitter 
disputes are reflex tears, generated by the main lacrimal glands in 
the upper, outer corner of your upper eyelid. When we cry, excess 
tears overflow down the cheeks while the rest flows through tiny tear 
drains into the nose and then into the throat. This explains the runny 
noise and the strange voice that we get when crying. Excessive crying 
may put strain on the lacrymal apparatus and create redness, or 
itchiness of the eyes. Rubbing the eyes to relieve this itch also 
contributes to redness and swelling. This is, however, only half the 
     In fact, the eyes and face become flushed and puffy because of the 
emotional response that always accompanies crying. To explain this, 
Iím afraid I have to say a few words about the human nervous 
system. In addition to our "voluntary" nervous system (which controls 
actions and thoughts), humans have two "autonomous" nervous 
systems, which control the parts of the body that work "by 
themselves", such as the heart or pancreas. The first one, called the 
parasympathetic nervous system, is controlled by parts of the brain 
responsible for our day-to-day involuntary bodily functions, such as 
digestion and breathing. The other, called the sympathetic nervous 
system, is controlled by centers of the brain and spinal cord that 
respond to stressful conditions, such as danger or strong emotions. 
When danger, anger or fear activates the sympathetic nervous 
system, we experience a "fight or flight" response. Adrenaline surges 
through our bodies, pupils dilate, the tear glands secrete more fluid, 
the heart begins pumping more blood more rapidly, breathing 
quickens, muscles tense, and our senses stand ready to respond to 
danger. The body reacts to any strong emotion, such as those that 
cause crying, in this way. The face becomes flushed and puffy from 
blood flow and from the facial muscular effort that crying generates. 

     Puffy eyes after a nightís sleep is easier to explain. It is most often 
related to drinking water late at night or having too much sodium in 
the diet, which causes water retention. Basically, it means that water 
has accumulated under the skin around the eyes. Such swollen eyes 
can also be caused by lack of sleep, too much alcohol, salt or 
caffeine, and there is also a genetic predisposition. As you will see 
on the internet if you type in "puffy eyes", many remedies are readily 

     I hope that this answers your question,
     Cheers !	

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