Botox injections are the best known of a group of medications that use various forms of botulinum toxin to temporarily paralyze muscle activity. This toxin is produced by the microbe that causes botulism, a type of food poisoning.Noted primarily for the ability to reduce the appearance of some facial wrinkles, Botox injections are also used to treat such problems as repetitive neck spasms (cervical dystonia), excessive sweating (hyperhidrosis), overactive bladder and some causes of crossed eyes. Botox injections may also help prevent chronic migraines in some people.While Botox was the first drug to utilize botulinum toxin, newer products include Dysport, Myobloc and Xeomin. Each product is a little different, particularly when it comes to dosage units, so they aren't interchangeable.

• Why it's done

Botulinum toxin injections block certain chemical signals from nerves, mostly signals that cause muscles to contract. The most common use of these injections is to temporarily relax the facial muscles that underlie and cause wrinkles, such as:

* Frown lines between the eyebrows
* Crow's-feet, the lines that fan out from the corners of the eyes
* Forehead furrows, the horizontal lines that form when you raise your eyebrows

In addition to these cosmetic procedures, which simply improve your appearance, botulinum toxin injections have also been used to treat conditions that affect how your body functions. Examples include:

* Cervical dystonia.
In this painful condition, your neck muscles contract involuntarily, causing your head to twist or turn into an uncomfortable position.

* Lazy eye.

The most common cause of lazy eye is an imbalance in the muscles responsible for positioning the eye. This can result in crossed eyes.

* Muscle contractures.
Some neurological conditions, such as cerebral palsy, can cause your limbs to pull in toward your center. In some cases, these contracted muscles can be relaxed with botulinum toxin injections.

* Hyperhidrosis.
In this condition, excessive sweating occurs even when the temperature isn't hot and you're not exercising. In some people, the sweat literally drips off their hands.

* Chronic migraine.
If you experience migraines more than 15 days a month, botulinum toxin injections may help reduce headache frequency. Bladder dysfunction. Botulinum toxin injections can also help reduce urinary incontinence caused by an overactive bladder.