The study, published in the January 2009 issue of the journal Chest, conducted tests on ferrets (who apparently have breathing organs very similar to humans), and found that Vicks VapoRub increased mucus production by up to 59 percent, and the ability to clear mucus was reduced by 36 percent.
The lead author, Dr Rubin explained in a statement to the Washington Post, that Vicks VapoRub can make some adults feel better without really making them better. "For kids, because it can induce some inflammation, even a little bit, that little bit might be enough to tip over a child to having problems," he said.
Here are some details from the abstract of the study:
"Vicks VapoRub (VVR) [Proctor and Gamble; Cincinnati, OH] is often used to relieve symptoms of chest congestion. We cared for a toddler in whom severe respiratory distress developed after VVR was applied directly under her nose. We hypothesized that VVR induced inflammation and adversely affected mucociliary function, and tested this hypothesis in an animal model of airway inflammation."
"Vicks VapoRub (VVR) stimulates mucin secretion and MCTV (tracheal mucociliary transport velocity) in the lipopolysaccharide-inflamed ferret airway. This set of findings is similar to the acute inflammatory stimulation observed with exposure to irritants, and may lead to mucus obstruction of small airways and increased nasal resistance."
Abanses J C, Arima S, Rubin B K. Vicks VapoRub Induces Mucin Secretion, Decreases Ciliary Beat Frequency, and Increases Tracheal Mucus Transport in the Ferret Trachea. Chest January 2009 vol. 135 no. 1 143-148
Vicks VapoRub is readily available over the counter to relive symptoms of cold and flu, but there is currently no research that suggests this salve has any respiratory health benefits. In fact, this study shows that in children, that it may worsen the very condition it is thought to help alleviate (relief of congestion and cough to provide free breathing).
Note: Vicks Vaporub (looking at the bottle right now) contains nutmeg oil (nutmeg is haraam). It also contains turpentine oil at a 5% w/w ratio. The manufacturer's recommendation is to put it into hot water and inhale the vapours, or to rub on the body and inhale the vapours.