Botox is the brand name in the United States of a form of bacterial poison called botulinum toxin type A. This substance causes botulism, a poisoning typically found in infected food. As Botox, however, the concentration is both low and purified.

Temporarily drooping eyelids, also known as transient ptosis, is the most commonly reported side effect of Botox according to the FDA-approved label. Approximately 5 percent of patients who receive Botox experience some degree of sagging in the eyelid area.

Dermatologists use Botox injections to reduce the appearance of wrinkles on the face. According to MayoClinic.com, Botox is derived from the botulism bacteria that causes food poisoning. After receiving a Botox injection, facial muscle cannot tighten, which causes skin to look smoother and tighter.