She’s giggling as she tells the joke. Like most of her jokes, this one just makes you want to groan and roll your eyes. Why does she find it so funny, but you can hardly muster a polite laugh? Experts say that several obvious differences in people affect what they find humorous. The most significant seems to be age. So that explains why you and your little sister don’t always laugh at the same things. Now, let’s take a closer look at what laughter is.

What Is Laughter?

Laughter is the physiological response to humor. It consists of two parts -- a set of gestures and the production of a sound. When we laugh, the brain pressures us to conduct both activities simultaneously. When we laugh heartily, changes occur in many parts of the body, even the arm, leg and trunk muscles. Fifteen facial muscles contract and stimulation of the zygomatic major muscle (the main lifting mechanism of your upper lip) occurs. Meanwhile, the respiratory system is upset by the epiglottis half-closing the larynx, so that air intake occurs irregularly, making you gasp. In extreme circumstances, the tear ducts are activated, so that while the mouth is opening and closing and the struggle for oxygen intake continues, the face becomes moist and often red (or even purple). The noises of laughter range from sedate giggles to boisterous guffaws. Now that we know what laughter is, let’s look at how it can be good for you.

Is Laughter Truly the Best Medicine?
We've long known that the ability to laugh is helpful to those coping with major illness and the stress of life's problems. But researchers are now saying laughter can do a lot more -- it can bring balance to all the components of the immune system, which helps us fight off diseases. Basically, laughter acts as a safety valve that shuts off the flow of stress hormones and the fight-or-flight compounds that swing into action in our bodies when we experience stress, anger or hostility. These stress hormones suppress the immune system and raise blood pressure. When we're laughing, natural killer cells that destroy tumors and viruses increase, as do Gamma-interferon (a disease-fighting protein), T-cells, which are a major part of the immune response, and B-cells, which make disease-destroying antibodies.

Furthermore, laughter may lead to hiccupping and coughing, which clears the respiratory tract by dislodging mucous plugs. Laughter also increases the concentration of salivary immunoglobulin A, which defends against infectious organisms entering through the respiratory tract. And, it has effects similar to exercise: researchers estimate that laughing 100 times is equal to 10 minutes on the rowing machine or 15 minutes on an exercise bike. It’s amazing that laughing can be a total body workout!

Photo credit © Michael Stuckey/Comstock/Corbis

• Figure out what makes you laugh and do it (or read it or watch it) more often.
• Surround yourself with funny people -- be with them every chance you get.
• Develop your own sense of humor. Maybe even take a class to learn how to be a better comic -- or at least a better joke-teller at that next party. Be funny every chance you get -- as long as it's not at someone else's expense!