Botox injections employ the most dangerous naturally occurring toxin: the Botulinum toxin. It is the trademark of Clostridium botulinum bacterium and less than 2 kg (5 pounds) would be enough to wipe out the whole human population (the botulinum toxin is 40 million times more powerful than cyanide). But in extremely small amounts, this toxin has medical and cosmetic employments (under the more familiar name Botox).

When the bacteria manage to enter a living animal, through contaminated food or open wounds, it triggers botulism, a severe infection that can easily kill children. If the bacteria manage to kill the host with their toxin, they get a new food source. Botulinum toxin is neurotoxic: it stops nerves and muscular contraction (this is also the mechanism by means of which the wrinkles' muscles relax). Injected tiny doses of botulinum paralyze a muscle for 4-6 months, a good method for a temporary elimination of facial wrinkles, but deadly if the toxin reaches the wrong muscles, like the heart.

Now, the US drugs safety watchdog Friday warned that Botox treatments can cause severe side-effects including death.

"The FDA has received reports of systemic adverse reactions including respiratory compromise and death following the use of botulinum toxins. The reactions reported are suggestive of botulism, which occurs when botulinum toxin spreads in the body beyond the site where it was injected. The most serious cases had outcomes that included hospitalisation and death," a statement issued by the Food and Drug Administration (FDA) said.

The botulinum toxins are used in both adults and children to treat various conditions, including spasms of the legs, eyelids or neck, the easing of facial lines, or excessive sweating.

US Advocacy group Public Citizen called last month for the FDA to "immediately increase its warnings ... about the use of botulinum toxin" because of "serious adverse reactions, including deaths, linked to the drug. Between November 1997 and December 2006 there were 16 deaths among the 658 reported cases of people suffering adverse effects from injections of botulinum toxin."

But FDA has "not concluded there is a causal relationship between the drug products and the emerging safety issue and it is not advising healthcare professionals to discontinue prescribing these products. FDA is considering, but has not reached a conclusion about whether this information warrants any regulatory action," the statement issued on Friday said.