Q. With the recent increase in use of sanitizers (hand lotions, wipes for supermarket carts, etc.) has there been any real impact on transmission of colds, flu or other diseases?

A. The short answer is no one knows, because no one has studied whether hand sanitizers have cut down on the number of infectious diseases among the public at large.

On a personal level, good hand hygiene clearly can make a difference in health. A 2008 study in The American Journal of Public Health concluded that improvements in hand hygiene, regardless of how the participants cleaned their hands, cut gastrointestinal diseases by 31 percent, and respiratory infections by 21 percent.

The key to stopping disease is breaking the chain that allows pathogens to be transmitted from person to person. Either hand washing or sanitizing can do that.

Sally Bloomfield, an expert in hand hygiene and an honorary professor at the London School of Hygiene and Tropical Medicine, said she always carries hand sanitizer with her when she travels. “London airport bathrooms are usually fine because they are well designed to make sure we wash our hands properly — and dry them properly,” she said, but some train “loos” leave something to be desired.

Grocery carts can be particularly risky points of transmission. Someone grabbing chicken or meat can leak the juices onto a cart and their hands, and then continue to push the cart around, transmitting pathogens like Salmonella and E. coli onto the handle. The next person who handles the cart, or the next child who sits in the top of the wagon, can then pick up the bugs.

“If you can wipe down the handle bars on the shopping cart with an alcohol-containing preparation, that’s probably a good idea,” said Dr. Cody Meissner, chief of the division of pediatric infectious disease at Floating Hospital for Children at Tufts Medical Center in Boston.

That said, Dr. Meissner and others cautioned against germaphobia. Every surface around us is coated in bacteria and other microbes, the vast majority of which are neutral or beneficial, said Liz Scott, chairwoman of the department of public health at Simmons College in Boston.

“We really need to target our hygiene practices,” she said, focusing on likely chains of transmission. That means washing your hands when you get back from the grocery store, public transit or any other public place, said Dr. Scott, who also admits to avoiding handshakes whenever possible, especially during flu season.