Why does ultrasound gel feel cold on the skin?
One of the comments you might hear from someone who has undergone an ultrasound procedure is that the gel feels cold on their skin. Ask an expectant mother about her experience with ultrasound gel and you will often hear that its coldness caused her to flinch.
Ultrasound gel is a water-based product and, over time, water acclimates to the temperature of its ambient environment. An average thermostat setting for an air-conditioned room is 78°F (26°C).1 If ultrasound gel is stored and used in a place that is air-conditioned, the gel’s temperature will become about the same as the room. Since average human body temperature is 98.6°F (37°C), the gel, in comparison, will feel much cooler to most people.
In addition, ultrasound gel that has been kept in a cool environment will take some time to lose that coolness. Water has a very high specific heat capacity, meaning that a defined amount of energy is required just to raise the temperature by one degree.2
Many practitioners warm ultrasound gel for the comfort of their patients. Typically gel warmers bring gel to average body temperature so the patient does not experience the feeling of cold on their skin. The practice of warming gel, however, is not recommended on a regular basis and shouldn’t be extended over long periods of time due to infection control concerns.3
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- 1. Energy.Gov, Thermostats. U.S. Department of Energy, Washington, DC., June 2012. http://energy.gov/energysaver/articles/thermostats
- 2. Freeman, Shanna. How Water Works. HowStuffWorks, Inc., 2013. http://science.howstuffworks.com/environmental/earth/geophysics/h2o7.htm
- 3. CHICA-CANADA Position Statement, Medical Gels. March 2005. http://www.chica.org/pdf/medgels.pdf