A leading expert has suggested people unconsciously recreate facial expressions in the area where the facial muscles have been paralysed.

This can sometimes cause other nearby muscles to compensate, which in turn can create new wrinkles.

This treatment has been proven safe and effective by multiple clinical studies Allergan spokeswoman

Dr David Becker, an assistant professor of dermatology at Weill Cornell Medical College in New York, said doctors and patients should be aware of these risks when starting treatment.

Surgery risks

He highlighted the risks of having botox injected between the eyebrows, which is one of the most popular areas for treatment.

"In this case, following treatment, muscles in the upper nose, middle eyebrow and eyelid may try to recreate the expression of a scowl. Repetitions of this action cause new wrinkles," he said.

He stressed that Botox had been proven to be a safe and effective treatment for wrinkles and any new lines were usually less prominent.

But he said if they did develop, the patient and their doctor would need to decide whether to discontinue treatment or use Botox elsewhere.

Botox, which is derived from the botulinum toxin A, is injected into the skin and works by temporarily paralysing muscles.

Injections take effect about three to seven days after treatment and the effect lasts three or four months.

A treatment costs roughly �200. With repeated treatments, atrophy or thinning of the muscles occurs, which produces longer lasting results.

Botox was licensed for use in cosmetic operations by the US Food and Drugs Administration last year.

It is not yet licensed for such use in the UK, which means doctors are free to use it but must be personally responsible for any ill-effects.

A spokeswoman for Allergan, which manufactures botox, said the treatment was safe.

"This treatment has been proven safe and effective by multiple clinical studies," she said.

The study is published in the journal Cosmetic Dermatology, which is the official publication of the American Society of Cosmetic Dermatology and Aesthetic Surgery.