Extremis is an advanced form of genetic manipulation created by Maya Hansen and Aldrich Killian, using nanotechnology. It grants the human body the ability to heal and regenerate from physical damages, deformities and even psychological damages.

Does Tony Stark have Extremis?

After his moral inversion, Tony Stark created a new Extremis called "Extremis 3.0" that grants the following abilities: Appearance Alteration: It allows people to have a form of shape-shifting, as they can alter their appearance to their own desires.

How did Pepper Potts get rid of Extremis?

During the crisis surrounding the Mandarin's terrorist attacks, Potts was kidnapped by Aldrich Killian and injected with Extremis. She was freed by Stark during the Battle on the Norco and went on to kill Killian herself. Stark cured her of the effects of Extremis, who temporarily gave up being Iron Man just for her.