The M-Pox is the name given to the condition that afflicts mutants upon entering in contact with excessive amounts of the Terrigen Mist, a substance better known for being the power source of the Inhumans.
When the villainous Thanos invaded the Earth looking for his bastard son Thane of Inhuman descent, the Inhuman king Black Bolt released massive amounts of Terrigen Mists into Earth's atmosphere through the activation of a Terrigen Bomb to empower every person on the face of the planet with Inhuman lineage. After spreading across the face of Earth, the Terrigen Mists settled in the form of two enormous clouds that roamed the planet, propelled by natural wind currents.
The molecular composition of the mists changed after being mixed with the atmosphere, turning the Terrigen Mists into a substance toxic for mutants. Because in the past mutants had been exposed to Terrigen Mists with no ill effects, for many months both mutant and Inhumankind were unaware of the negative effects the Terrigen Clouds until Cyclops and a group of X-Men heeded an emergency call from Muir Island, which had been struck by one of the clouds, and discovered its staff dead. With his final breaths, the agonizing Multiple Man informed Cyclops it was discovered the Mists were harmful, albeit too late for them.
Storm soon informed the Inhuman queen Medusa about this development, and the X-Man biophysicist Beast agreed to stay with the Inhumans in New Attilan in order to find a cure for this predicament. Almost immediately, Emma Frost divulged to the entire world that the Terrigen Mists were harmful to mutants.
Over the following months, millions of mutants began to fall ill to the M-Pox, endangering mutantkind as a species. Eleven crisis medical centers were established around the world to treat mutants that were suffering from M-Pox, including three in the United States. One of them located in Kansas City; Missouri, and another in Seattle; Washington.
People around the world reacted differently to the presence of the M-Pox. Popular opinion believed the M-Pox to be contagious, which fueled the fires of anti-mutant hysteria, manifested in the form of protests and discrimination. In the worst of the cases, members of both the sick and healthy mutant population were prosecuted and massacred by fanatics. Places where these tragedies happened included India,, Germany, and Colombia. The X-Men saw themselves forced to retreated to the extra-dimensional realm known as Limbo, creating X-Haven, a sanctuary for mutants from any part of the world. Numerous mutants retreated underground and joined the Morlocks to remain safe from the Terrigen Cloud, with some paranoid Humans following their steps, creating an unusual unification between those mutants and Humans that lived together in the Morlock Tunnels beneath Manhattan.
When Beast discovered that the Terrigen Cloud was weeks away from reaching a saturation point that would've caused it to be entirely assimilated into the atmosphere, making the Earth uninhabitable for mutants, he shared this information first with the X-Men. Believing that the Inhumans would refuse to destroy the cloud even at this moment, the different factions of the X-Men united to launch a coordinated attack on Inhuman key players in order to neutralize them long enough, trapping most of them in Limbo, to use a machine created by Forge to absorb and destroy the Terrigen. Two of the newest Inhumans, Iso and Inferno, managed to escape the assault on New Attilan and destroy Forge's machine, taking him hostage.
The two young Inhumans then called reinforcements in the form of other NuHumans, including Mosaic,  who used his powers to infiltrate Muir Island and learn the X-Men's reason behind their attack, later reporting that to his peers, which prompted the NuHumans to join forces with Forge to come up with a new solution.
The NuHumans then travelled to Iceland, the latest location of the Terrigen Cloud, but were soon confronted by the X-Men, who had no idea of their plans. The royal Inhumans joined the brawl, having escaped from Limbo and regrouped. The battle was interrupted when Ennilux arrived, having provided Forge and Moon Girl with the resources to build the machine necessary to eliminate the Terrigen Cloud. Medusa was notified of what was at stake and given the trigger to activate the device. In spite of what the destruction of the Terrigen Cloud meant for Inhumans, Medusa activated the machine, destroying the Cloud and ending the threat of the M-Pox.
The prevalence of infection of the M-Pox is unknown, as it affects mutants to varying degrees. Some die upon immediate contact with Terrigen Mists, others succumb to the passage of time, and some fortunately seem to remain unaffected. Initial symptoms include coughing fits and dizziness. As the illness progresses, the victim develops boils, and their immune system becomes compromised. In the final stages before death, victims collapse, and ultimately bleed out. M-Pox also sterilizes its victims.
The progress of the M-Pox can be slowed down by chemical compounds, and people with healing powers; however, the Terrigen Mists creates a specific reaction unique to each X-Gene it enters into contact with, rendering it an impossible task to create a universal cure. Powerful healers like the resurrected Elixir could potentially rid a victim of M-Pox altogether, though at great cost to themselves and anyone in the surrounding area. Also, mutants with healing factors, like Logan, appear to be more resistant to the deleterious effects of the Terrigen Mists, as they will recover eventually.
- Multiple Man (Jamie Madrox) (deceased, later resurrected)
- Cyclops (Scott Summers) (deceased, later resurrected)
- Goldballs (Fabio Medina) (treated in time and seemingly cured)
- Alchemy (Thomas Jones) (deceased)
- Sunspot (Bobby Da Costa) (under treatment, later cured)
- Rogue (Anna Marie) (under treatment, later cured)
- Sapna (deceased, due to unrelated reasons)
- Dazzler (Alison Blaire) (later cured)
- Thor (Alison Blaire) (disappeared upon contact with the Terrigen Cloud)
- Lady Mastermind (Regan Wyngarde) (under treatment, later cured)
- Ronnie (under treatment)
- Lucid (Maya Jackson) (deceased)
- 10 appearance(s) of M-Pox
- 40 minor appearance(s) of M-Pox
- 31 mention(s) of M-Pox
- 1 image(s) of M-Pox