Will putting people's hands in warm water really make them wet the bed?

Tales of summer camp and slumber party pranks are as plentiful (and exaggerated) as fishing stories. We've all heard of the short-sheeted bed or of the combined power of a handful of shaving cream and a feather. But how much should we believe the ultimate cautionary tale against being the first to fall asleep: making someone wet the bed by placing his or her hand in a pan of warm water? Should we accept the steady stream of reported successes, or seek the truth in the annals of scientific research, which scarcely mentions the phenomenon?

Enter the producers of "MythBusters," to whom rampant anecdotal evidence is a call to action. In episode 136, "Mini Myth Mayhem," the hosts tested the time-honored tinkle trick on hosts Adam and Jamie and on a crew member named Matt. Relying on a moisture sensor to detect any urinary mishaps and sleep monitoring equipment to ensure each subject had slipped into solid sleep, they dunked, dipped and dripped their way to a negative result: Not one of the three subjects wet himself when his hand went for a moonlight swim.

But numerous experimental design flaws and problems left their result circling the drain. Beyond the distorting influences of their very small sample size and, worse, of using subjects who knew that they were being observed and were aware of the experiment's goals, Jamie never achieved sleep, Adam was repeatedly awoken by his sleep apnea and Matt activated his wetness alarm with spilled water. Moreover, Adam's hand position kept Jamie from dousing it with more than a drizzle [source: MythBusters].

So, attempts at answering the question experimentally are hardly flush with success. Could there be a theoretical basis for believing the prank is possible? Immersion of the lower body and use of warm water bottles have been shown to relieve post-surgical urinary retention, but a damp hand is a far cry from a wet bottom. On the other hand, the power of suggestion might hold some explanatory promise; many people with medically or socially shy bladders successfully use the sound or image of running water to open the floodgates.

We'll examine both immersion and suggestion in detail in the next section, and ask the related question: What role does sleep play in the equation?

Go With the Flow

If the soaking hand prank works, then how does it overcome the mechanisms we develop in childhood to prevent bed-wetting (see sidebar)?

Our bodies store urine in the bladder, a muscle bag that retains liquid by relaxing and expels it by contracting. Outbound urine streams through a tube called the urethra. To help the process of retention and release, muscles squeeze the urethra shut at two points: the bladder neck, aka the internal urinary sphincter, and the external urinary sphincter, located a bit further down.

Medically, the trick to overcoming postoperative retention lies in convincing these sphincters to relax. Studies suggest that sitting in a warm water bath or placing a hot water bottle on the pelvis can do just that, likely through a temperature-based sphincter reflex [sources: Elsamra and Ellsworth; Kulaçoğlu et al.; Shafik].

"Heat and warm water is a common relaxation modality," says Valre Welch, a pediatric nurse practitioner and past president of the Society of Urologic Nurses and Associates.

"It encourages blood flow, and it's very soothing after genital surgery."

But would the same reflex hold true when dunking, not the affected area, but a hand or a few fingers? The answer is a firm perhaps, if the paw plunge is combined with a very deep sleep and/or the power of suggestion.

Research bears out the power of watery images or sounds to instill a sense of urinary urgency [source: MUCMN]. Moreover, it makes sense: The inhibition and release of the micturition reflex -- the contraction of bladder walls and relaxation of urethral sphincters in response to bladder pressure -- is controlled by the brain and nervous system.

As pressure builds inside the bladder, the rate of nerve impulses flowing from it to the spinal cord surges. Neurons in the spinal cord then send signals to brain areas called the pons and cerebrum, which make us feel a conscious desire to pee. If for some reason urination isn't in the cards, the brain RSVPs with a polite "no" and signals via the spinal cord for the bladder to inhibit the reflex. Later, when it's go time, the brain sends signals that activate the micturition reflex, and it's a potty in the USA [source: McKinley and O'Loughlin].

During a typical night's sleep, a full bladder kicks off like an abdominal car alarm. It needles us until we wake up and take care of business. But get a little too drunk, stoned or exhausted, and you might just ignore that alarm -- especially if the power of suggestion relaxes you further via a pan of warm water.

"It really does occur," says Welch. "It is a phenomenon of relaxation."

Lots More Information

Author's Note: Will putting people's hands in warm water really make them wet the bed?

So there you have it. The hand-in-water trick is no longer a debate with no relief in sight. Or is it? Whether confirmed or refuted, these arguments never seem to die. In the end, if you want to plumb the mysteries of the ages, you'll just have to take the plunge yourself.

Sources

Boyse, Kyla. "Enuresis (Bed Wetting)." University of Michigan Health System. September 2008. (Jan. 17, 2014) http://www.med.umich.edu/yourchild/topics/enuresis.htm
Elsamra, Sammy E. and Pamela Ellsworth. "Effects of Analgesic and Anesthetic Medications on Lower Urinary Tract Function." Urologic Nursing. Vol. 32, no. 2. Page 60. 2012. (Jan. 9, 2014) http://www.medscape.com/viewarticle/763040_2
Hagopian, Louis P., Wayne Fisher, Cathleen C. Piazza, and John J. Wierzbicki. "A Water‐Prompting Procedure for the Treatment of Urinary Incontinence." Journal of Applied Behavior Analysis. Vol. 26, no. 4. Page 473. 1993. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1297874/pdf/jaba00014-0066.pdf
Kulaçoğlu, Hakan, Cenap Dener and Nuri Aydın Kama. "Urinary Retention After Elective Cholecystectomy." American Journal of Surgery. Vol. 182, no. 3. September 2001. (Jan. 9, 2014) http://www.sciencedirect.com/science/article/pii/S0002961001007036
McKinley, Michael and Valerie Dean O'Loughlin. "Human Anatomy." McGraw-Hill. 2006. (Jan. 17, 2014) http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter27/animation__micturition_reflex.html
Metropolitan Urology Clinic (Minneapolis, St. Paul). "Do You Have an Overactive Bladder? (Urge Incontinence)." (Jan. 17, 2014) http://www.mucmn.com/overactive-bladder/
MythBusters. "Hand In Water While Asleep Makes You Urinate; Finding: Busted." Dec. 28, 2009. (Jan. 9, 2014) http://dsc.discovery.com/tv-shows/mythbusters/mythbusters-database/hand-water-asleep-urinate.htm
Shafik, Ahmed. "Role of Warm Water Bath in Inducing Micturition in Postoperative Urinary Retention After Anorectal Operations." Urologia Internationalis. Vol. 50, no. 4. 1993. (Jan. 9, 2014) http://www.karger.com/Article/Abstract/282487
Welch, Valre, pediatric nurse practitioner; secretary and past president of SUNA, the Society of Urologic Nurses and Associates. Personal interview. Jan. 24, 2014.