TUESDAY, Feb. 8 (HealthDay News) -- An injection of local anesthetic can be made much less painful if it is warmed beforehand, Canadian researchers report.

They reviewed 18 studies that included a total of 831 patients and found that pre-warming injections led to a "clinically meaningful reduction in pain," regardless of: whether the anesthetic had been buffered or not; whether the shot was administered subcutaneously (under the skin) or intradermally (into the skin); or whether the amount injected was large or small.

The injections were warmed a number of ways, including controlled water baths, incubators, fluid warmers, baby food warmers, a warming tray and a syringe warmer.

There are anecdotal reports that some emergency doctors use their hands to warm injections, according to the study published online Feb. 8 in the Annals of Emergency Medicine.

"Warming an injection is a cost-free step that emergency physicians can take to reduce pain from a shot," lead author Dr. Anna Taddio, of the University of Toronto, said in a journal news release.

"Patients often dread the sight of a needle, but doing something as simple as warming the injection to body temperature can make a painful part of an emergency department visit more tolerable," Taddio explained.

She said future research should look at the effects of warming local anesthetics for dental procedures and child-specific procedures.

"This is an area where a small change may make a big difference for a patient," Taddio said.

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