Some people who chew areca nuts could be genetically more prone to mouth cancer, a study shows.
Chewing the nut, also known as the betel, is popular in Asia and among UK Asians as it contains arecoline - a stimulant thought to improve memory.
All areca-nut chewers have an increased chance of mouth cancer.
But scientists at Taiwan's National Yang-Ming University found variations in the HO-1 gene can increase the risk of developing cancer two-fold.
The team looked at variations of the HO-1 gene in 147 areca chewers with mouth cancer, 71 with oral submucous fibrosis, a scarring condition of the mouth, and 83 people without mouth cancer.
Tumour
They found a certain variation of the gene was much more common in men with mouth cancer, according to the findings in the British Journal of Cancer.
The gene helps to protect cells from damage by harmful agents such as UV irradiation or hydrogen peroxide.
But studies have also suggested that it may be involved in promoting tumour growth and maintaining cancer survival.
More than 153,000 cases of mouth cancer are diagnosed in Asia each year while 4,300 cases are found in the UK.
Lead researcher Dr Shu-Chun Lin said: "We know that chewing areca nuts increases a person's risk of mouth cancer.
"But not everyone who takes up the habit develops mouth cancer so there must be genetic factors involved.
Risk
"Particular variations of the gene have been associated with an increased risk of heart or lung disease.
"This is the first study to look at whether different forms of the gene affect mouth cancer risk."
Areca nut chewing is particularly common in men, with as many as one in five chewing it in areas of Asia.
Dr Lesley Walker, director of cancer information at Cancer Research UK, urged people to be wary of chewing areca nuts.
"We know that areca chewers run the risk of getting mouth cancer. This report suggests that if people chew areca and also possess this particular gene variant - their risk of the disease is even higher.
"Most cases of cancer are caused by a combination of genetic and environmental factors.
"It's important to remember that habit and lifestyle can have a big effect on the risk of mouth cancer.
"The best way to prevent the areca-related mouth cancer is to avoid chewing the nut on its own or in combination with tobacco."