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Why Do People Faint?


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Reasons Why You Might Swoon

Here are some of the reasons why teens faint:

  • Physical triggers. Getting too hot or being in a crowded, poorly ventilated setting are common causes of fainting in teens. People can also faint after exercising too much or working out in excessive heat and not drinking enough fluids (so the body becomes dehydrated). Fainting also can be triggered by other causes of dehydration, as well as hunger or exhaustion. Sometimes just standing for a very long time or getting up too quickly after sitting or lying down can cause someone to faint.
  • Emotional stress. Emotions like fright, pain, anxiety, or shock can affect the body's nervous system, causing blood pressure to drop. This is the reason why people faint when something frightens or horrifies them, like the sight of blood.
  • Hyperventilation. A person who is hyperventilating is taking fast breaths, which causes carbon dioxide (CO2) to decrease in the blood. This can make a person faint. People who are extremely stressed out, in shock, or have certain anxiety disorders may faint as a result of hyperventilation.
  • Drug use. Some illegal drugs (like cocaine or methamphetamine) or using inhalants ("huffing") can cause fainting.
  • Low blood sugar. The brain depends on a constant supply of sugar from the blood to work properly and keep a person awake. People who are taking insulin shots or other medications for diabetes can develop low blood sugar and pass out if they take too much medicine or don't eat enough. Sometimes people without diabetes who are starving themselves (as with crash dieting) can drop their blood sugar low enough to faint.
  • Anemia. A person with anemia has fewer red blood cells than normal, which decreases the amount of oxygen delivered to the brain and other tissues. Girls who have heavy periods or people with iron-deficiency anemia for other reasons (like not getting enough iron in their diet) may be more likely to faint.
  • Pregnancy. During pregnancy the body normally undergoes a lot of changes, including changes in the circulatory system. This leads to low blood pressure that may cause a woman to faint. In addition, the body's fluid requirements are increased, so pregnant women may faint if they aren't drinking enough. And as the uterus grows, it can press on and partially block blood flow through large blood vessels, which can decrease blood supply to the brain.
  • Eating disorders. People with anorexia or bulimia may faint for a number of reasons, including dehydration, low blood sugar, and changes in blood pressure or circulation caused by starvation, vomiting, or overexercising.
  • Cardiac problems. An abnormal heartbeat and other heart problems can cause a person to faint. If someone is fainting a lot, especially during exercise or exertion, doctors may suspect heart problems and run tests to look for a heart condition.


Can You Prevent Fainting?

Bagging Hyperventilation



  • If possible, lie down. This can help prevent a fainting episode as it allows blood to circulate to the brain. Just be sure to stand up again slowly when you feel better — move to a sitting position for several minutes first, then to standing.
  • Sit down with your head lowered forward between your knees. This will also help blood circulate to the brain, although it's not as good as lying down. When you feel better, move slowly into an upright seated position, then stand.
  • Don't let yourself get dehydrated. Drink enough fluids, especially when your body is losing more water due to sweating or being in a hot environment. Drink enough fluids before, during, and after sports and exercise.
  • Keep blood circulating. If you have to stand or sit for a long time, periodically tense your leg muscles or cross your legs to help improve blood return to the heart and brain. And try to avoid overheated, cramped, or stuffy environments.

What Should You Do?



What Do Doctors Do?




Helping Someone Who Faints





Reviewed by: Mary L. Gavin, MD
Date reviewed: February 2014

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