Itching to stop smoking? 

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Scientists think they have discovered why people trying to quit smoking often find they are itching to stop.

Belgian researchers studying the effect of nicotine in mice found that it activates a molecular pathway in membranes in the skin, nose and mouth known to play a role in inflammation.

This may explain why nicotine patches and other nicotine replacement therapies can make people itch, they said in a study published in Nature, and could help in developing treatments to help people quit smoking with fewer irritating side effects.

Smoking is one of the biggest causes of disease and premature death worldwide and smoking-related illness costs health services billions of dollars each year.

British researchers reported in April that smokers who do not yet want to quit but are prepared to smoke less are twice as likely to stop eventually if they use nicotine replacements to help cut down gradually.

US research suggests the average smoker tries between six and 11 times to quit.

Until now, scientists had thought that irritation from nicotine patches and other nicotine treatments came from stimulation of nerve receptors that convey painful stimuli from the skin and the linings of the nose and mouth.

But Karel Talavera of the Leuven Catholic University in Belgium found that in mice, nicotine also directly activates TRPA1, a pathway or channel in cells known to convey information about irritating substances and inflammatory pain.

They also found that mice lacking TRPA1 showed no irritation when nicotine was put into their noses.

"The identification of TRPA1 as a nicotine target ... may facilitate the development of smoking cessation therapies with less adverse effects," the researchers wrote.