Scientists in Europe said they could explain why nicotine patches designed to help smokers kick their habit can cause skin irritation.
Nicotine activates a so-called ion channel in skin cells that unleashes an inflammatory response by the immune system, leading to itching, they reported in the journal Nature Neuroscience.
Previously, the irritation had been blamed on stimulation of special nicotine receptors on nerve cells, causing pain signals to be sent to the brain.
The investigation, carried out on mice that had been genetically modified to lack the TRPA-1 ion channel, was led by Karel Talavera of the Leuven Catholic University, near Brussels.
The discovery could pave the way to smoking therapies with fewer side effects, the authors say.