Q&A: The science behind weird body reactions

By Mayo Clinic Health System staff

Every day our bodies do some rather strange and unusual things. Here are some questions and answers including the science behind why these happen.

Q. Why do fingers wrinkle in water?

A. Initially, the thought was that fingers wrinkled in water because of the fluid shifts that occur through the tissues and the surrounding water. Now, evolutionary experts are finding evidence that it may have actually helped humans to grip objects better when in water. People who have nerve damage to their fingers or toes often will not have this same wrinkling of fingers.

Q. Why can I sometimes hear a pulse in my ears?

A. You feel a pulse in your ears for a variety of reasons. Tinnitus is often described as a ringing in the ears, but there is a variation where you can feel and hear the pulse in your ears. This is called "pulsatile tinnitus." Elevation in blood pressure or blockage of the ear canal can cause you to hear your pulse. An abnormality of the arteries by the ears also can cause this sensation. This is definitely a reason to talk to your primary care provider.

Q. Why do I shiver when it’s cold?

A. You shiver when you are cold because this is a way to quiver your muscles in an effort to create heat. Your body is always trying to keep its temperature as close to 98.6 degrees F as possible.

Q. Why do some people sneeze when they look up at the sun?

A. This is called the "photic sneeze reflex," with the nickname “sun sneeze.” The theory is that the optic nerve, which senses a change in light, is close to the trigeminal nerve, which controls a sneeze. A typical sneeze is caused by irritation in the nose which fires the trigeminal nerve to trigger a sneeze. When you step out of a dark room and into bright light, the pupils constrict. This reflex is triggered by the optic nerve. The rapid triggering may give the sensation that there is an irritation in the nose and thus trigger the sneeze. Interestingly, not everyone has this reaction. There is no known reason why some people have it and other people do not.

Q. Why do I get a stitch in my side from running?

A. A side stitch is caused by irritation to the diaphragm — the muscle that separates the lung and abdominal cavities. Novice runners are more apt to get side stitches than experienced runners. Sometimes it is caused by too-rapid breathing or an inappropriate meal eaten before running.

Q. Why does my eyelid randomly twitch?

A. Twitching of the eyelid is called "blepharospasm." It is not known why this happens exactly, but fatigue, caffeine and stress are common culprits. I often recommend trying to stretch the muscle that is twitching. Typically the twitching goes away on its own. If the twitching lasts more than a couple of days, it is important to seek evaluation from your primary care provider.