It’s time for hospital accreditation week, and you have removed the posters from the walls, had all of the computers PAT tested, and the team has even completed their mandatory competencies. The Infection Control team does a final sweep of the department and makes sure the alcohol hand rub dispensers are in a perfect position. As you lead them out, you hear a giggle from one of the cubicles, followed by a slow drifting stream of iridescent bubbles.
“Bubbles? Bubbles! Get them out of here! They are harbouring all sorts of germs!”
Is this political correctness gone mad, or is there something in it
How do bubbles form?
Way back in 1888, K. Herman Schwartz proposed that a bubble is the minimal surface area way of enclosing a given volume of air. This surface is made up of a thin layer of water molecules sandwiched between two layers of soap molecules. When two bubbles meet they merge walls to maintain their minimal surface area.
When they pop, according to researchers at MIT, water evaporates from the cap of the bubble, cooling its surface temperature compared to the base (imagine a bubble on a flat plate). There is then a difference in surface tension at the base and the cap, driving water upwards to the cap. This is known as Marangoni flow. If this occurs on the surface of water, the bubble may only last for a few seconds. High-speed cameras capturing the event reveal they pop into 10-15 droplets. But if it takes place on a not-so-clean surface, the bubbles can last much longer and explode into 250 or more tiny droplets.
Can you grow bacteria on bubbles?
Absolutely! Though you may think that soap helps get rid of bacteria, consider what the soap solution is made of. If contaminated water is used, then it is certainly possible to grow bacteria in a bubble. The commonest organism grown is Pseudomonas aeruginosa, followed by Escherichia coli.
The formation of a biofilm on the surface of a bubble extends its life. As we saw earlier, these bubbles explode, creating ten times as many droplets as sterile bubbles. They also expulse ten times faster from bacteria-laden bubbles than clean ones—up to 15 m/s. Does this make a bubble the ultimate bacterial dispersal system?
So, can they cause harm?
McGarrity and Coriell showed experimentally that if you blow bubbles using a contaminated sample, bacterial isolates can be collected from the bubble artist’s face and hands. They remained on non-porous surfaces for up to 30 minutes. The question then becomes, just how many products are contaminated?
An enterprising nurse epidemiologist found that 38 out of 75 (50.6%) solutions were contaminated in the Children’s Hospital in Denver in 2005. This led to the wholesale removal of them from the paediatricians’ repertoire while a safer alternative was found. It seems that pinwheels and party blowers just don’t cut it with the kids, and so it was back to soap and water.
This also proved to be a problem in 2012 when three children developed sepsis when playing with a contaminated bubble-blowing toy. They had been playing happily in the morning and, by the evening, had developed a sore throat, limb pain, and a fever. The soap solution was the most likely culprit, and an Italian team of investigators traced the soap products back to a couple of manufacturing zones in China.
Are bubbles really that bad?
Bubbles have been a source of wonderment for over 400 years. Paintings by Flemish artists such as Adriaen Hanneman and Jean-Etienne Liotard show children blowing bubbles with smiles on their faces.
In the emergency room, they are routinely used as a distraction from potentially painful procedures or as a means to assess a pre-verbal child. If they can track and follow, reach out to grab and smile, then they are on the right track.
But in this time of full PPE for aerosol-generating procedures, perhaps it is best to leave your bubble-blowing exploits at home.
The best bubble mix?
Here are your basic ingredients:
- 1 cup of liquid dish soap
- 6 cups of distilled water
- 1 tablespoon of glycerin
Pour the dish soap into the water and gently mix it (try not to make any bubbles!). Then add in the glycerin and stir. Put the lid on the container and leave it overnight before use.
Selected references
Amoruso I, Bertoncello C, Caravello G, Giaccone V, Baldovin T. Child toy safety: An interdisciplinary approach to unravel the microbiological hazard posed by soap bubbles. Journal of Public Health Policy. 2015 Nov 1;36(4):390-407.
Caprilli S, Vagnoli L, Bastiani C, Messeri A. Pain and distress in children undergoing blood sampling: effectiveness of distraction with soap bubbles: A randomized controlled study. Children’s Nurses: Italian Journal of Pediatric Nursing Science/Infermieri dei Bambini: Giornale Italiano di Scienze Infermieristiche Pediatriche. 2012 Mar 1;4(1).
Dolan SA, Eberhart T, James JF. Ask the Expert: Bubbles to Wubbles™: An Investigation Involving the Contamination of Soap Bubble Products at a Pediatric Hospital. Journal for Specialists in Pediatric Nursing. 2006 Jul;11(3):189-95.
Helmenstine, Anne Marie, Ph.D. “What’s the Science Behind Bubbles?” ThoughtCo, Feb. 11, 2020, thoughtco.com/bubble-science-603925.
H. Lhuissier, E. Villermaux, “Bursting bubble aerosols,” J. Fluid Mech. 696, 5 (2012)
Maghsoudi S, Sajjadi Z, Behnam Vashani H, Asghari Nekah SM, Manzari ZS. Comparison of the effects of play dough and bubble-making distraction techniques on venepuncture pain intensity in children. Evidence-Based Care. 2016;5(4):25-32.
McGarrity GJ, Coriell LL. Bacterial contamination of children’s soap bubbles. American Journal of Diseases of Children. 1973 Feb 1;125(2):224-6.
Oliveira NC, Linhares MB. Nonpharmacological interventions for pain relief in children: A systematic review. Psychology & Neuroscience. 2015 Mar;8(1):28.
Poulain S, Bourouiba L. Disease transmission via drops and bubbles. Physics Today. 2019 May 1;72(5):70-1.
Sartor, C. (2000) Nosocomial Serratia marcescens infections associated with extrinsic contamination of a liquid nonmedicated soap. Infection Control and Hospital Epidemiology 21 (3): 196–199.
