Neurotoxins work on the nerve cells to prevent the conduction of nerve impulses to muscle.
“Mechanism of Action. Botulinum toxin acts by binding presynaptically to high-affinity recognition sites on the cholinergic nerve terminals and decreasing the release of acetylcholine, causing a neuromuscular blocking effect.”
There are several different products approved by the FDA for the treatment of dynamic facial lines in the face, in particular, the frown lines (corrugators and procerus muscles) and crow’s feet (orbicularis oculi muscle). The most common products are Botox®, Dysport® and Xeomin®. All of these are diluted with normal saline and injected into facial muscles in small amounts to paralyze the muscles. They all act in a delayed fashion generally taking about 3-5 days to fully take effect. The most common areas to treat are the frown lines between the eyebrows, and the crow’s feet at the sides of the eyes. The horizontal ‘worry’ lines on the forehead (frontalis muscle) are a common treatment site but are considered ‘off-label’ by the FDA. Treating the frown lines and the crow’s feet helps to elevate the eyebrows.
Injecting around the lower eyelids (crow’s feet) can widen the eyes (palpebral fissure). Other areas where toxins are helpful are various ‘off-label’ treatments such as injecting the depressor anguli oris muscle, which pulls down the angle s of the mouth. Injecting this muscle at the jaw line can elevate the angles of the mouth. Injections at the base of the nose (depressor septi) can elevate the tip and prevent it dropping on smiling. ‘Bunny’ lines at the side of the nose (nasalis muscle primarily but also the procerus and levator labii superioris alaeque nasi) also be helped with toxin injections. Other uses of toxin injections are to prevent sweating of the arm-pits, scalp and palms. Injections into the playtysma bands at the front of the neck can make them less prominent. There are many uses for toxins both cosmetic and functional. Toxins are also used to treat trigger points in the head and neck area for the treatment of migraine headaches.