The botulin toxin, which is extracted from a bacterium, temporarily paralyses the facial muscles that cause wrinkles. It is particularly effective for lines in the forehead, frown lines and crow's feet. The results, which are noticeable four days after the injection, last for up to six months.
The toxin works by binding to receptor sites at the junction between nerve cells and facial muscle fibres, causing them to relax. It blocks a naturally occurring chemical, acetycholine, which makes muscle fibres contract. After the injection the skin sags slightly and the wrinkles fall away.
Monte Keen, director of facial, plastic and reconstructive surgery at the Columbia Presbyterian Medical Center, New York, who developed the technique, says that four injections are needed for forehead wrinkles and two for crow's feet or frown lines. In a recent trial of 12 patients, Dr Keen injected one half of the face with the toxin and the other with a salt solution. The toxin-injected halves showed fewer wrinkles, according to a report in New Scientist.
Each injection must be precisely placed and Dr Keen uses a probe connected to an electromyograph which measures the electrical activity of muscles. It records the highest reading when the muscle is reached. Only the upper two thirds of the face are suitable; injections too close to the eye can make the eyebrow droop if the wrong muscles are affected, and the top lip can become temporarily paralysed.
Botulin toxin comes from Clostridium botulinum and is one of the deadliest poisons known. It has been linked to fatal food poisonings. However, the toxin has been used for years by doctors to relax muscles in patients with facial palsy and eye squints.Reuse content