Skip to content

Forget the Bubbles!


It’s time for hospital accreditation week and you have taken the posters off of the walls, had all of the computers PAT tested and the team have even completed their mandatory competencies. The Infection Control team do a final sweep of the department and make 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?

K. Herman Schwartz proposed that a bubble is the minimal surface area way of enclosing a given volume of air back in 1888. 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 in order 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 when 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 seconds. High-speed cameras capturing the event reveal they pop into 10-15 droplets. But if it takes place on not-so-clean a surface the bubbles can last much longer and explode into 250 or more tiny droplets.

Can you grow bacteria on bubbles?

Absolutely! Though you might think that soap helps get rid of bacteria consider what soap solution is made of. If contaminated water is used then it is certainly possible to grow bacteria on 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 and as we saw earlier these bubbles explode creating 10 times as many droplets as sterile bubbles. They also expulsed 10 times faster from bacteria-laden bubbles than clean ones – up to 15 m/s. Does this make a bubble the ultimate bacterial dispersal system?

A bubble contaminated with bacteria (shown in the bottom panel) lasts much longer than a clean bubble. (Image: © Image courtesy Lydia Bourouiba and Stephane Poulain, Massachusetts Institute of Technology.)

So, can they actually cause harm?

McGarrity and Coriell showed, experimentally, that if you blew bubbles using a contaminated sample then bacterial isolates could be collected from the face and hands of the bubble artiste, and that they remained on non-porous for up to 30 minutes. The question then becomes, just how many products are contaminated?

An enterprising nurse epidemiologist, back in 2005, found that 38 out of 75 (50.6%) of solutions were contaminated in the Children’s Hospital in Denver. This led to wholesale removal of them from the paediatricians’ repertoire whilst 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 particular 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.

Children Blowing Bubbles by Jean-Etienne Liotard © Ali Meyer/CORBIS

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 for 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,

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.



No data was found