Nicotine patches can reduce cravings
Scientists say they have discovered why people who are trying to quit smoking can get an attack of the itches.
It appears that nicotine patches used to help smokers kick the habit activate chemical pathways in the skin, nose and mouth that play a role in inflammation.
The Belgian team, who studied the effects in mice, say their findings could help others develop smoking cessation aids with fewer side effects.
The results are published in the journal Nature Neuroscience.
Nicotine Replacement Therapy (NRT) gives the body nicotine without the harmful effects of smoking or chewing tobacco.
The idea is to gradually reduce the addiction by using a low nicotine dose to take the edge off the cravings.
People who use nicotine patches or gum double their chances of successfully quitting, experience shows.
But some do experience side effects with NRT.
Nicotine patches commonly cause skin irritation, and nicotine inhalers and nasal sprays may cause irritation in the mouth or nose.
Until now, scientists had thought that irritation came from stimulation of nerve receptors that convey painful stimuli from the skin and the linings of the nose and mouth.
But Dr Karel Talavera, of the Leuven Catholic University in Belgium, and colleagues 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.
Writing in Nature Neuroscience, they said: "Our results indicate that inhibition of TRPA1 represents an interesting approach for developing smoking cessation therapies with less adverse effects."
A spokesman for Action on Smoking and Health said: "Itchiness is a familiar problem with nicotine replacement patches, but there are lots of different products available, including prescription drugs.
"If for whatever reason your chose quit medicine is not working, speak to an advisor to discuss what remedy will be best for you."