Main Article Theories about
The Sickness
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The Man in Black is a carrier of the Sickness

The Man in Black is a prisoner of quarantine, because the Island's healing properties provide (mostly) a vaccination effect against the virus / plague the Man in Black is carrying. If the Man in Black were able to escape the Island, this would result in a worldwide and lethal pandemic and make the possible reunion of the Kwon family, as suggested by Widmore, a "short-lived" one.

Physical contact with the Man in Black / Smoke Monster will result in contagion (e.g. Rousseau's team) with only those previously touched by Jacob or subsequently Richard (the Others) remaining immune.

The Sickness is a result of absorbing more of The Source

Danielle had the sickness

She looked similar to Claire did after she caught it.


The blast door map

The blast door map contains the statement: "Aegrescit Medendo". Translation: "The remedy is worse than the disease". This refers to death being the "remedy" to the "disease". The poison pill Dogan offers is worse than the infection.

The Sri Lanka video

The sickness is the disease referred to in the Sri Lanka video by Mittelwerk, i.e., "They think they are infected by a virus carried by local macaques...", "We must make absolute certain we are hitting precise genetic targets...", "We need not take any more lives than is absolutely necessary. Yes?", and most importantly "...we have engineered into the virus."


The Sickness is "Malevolence"

"The Sickness" is that "evil" that the Island keeps in line, some it sometimes "slips through the cracks".


Claire and Sayid, though infected, rebelled against the Man in Black. This proves the Sickness is reversible.

A "Zombie" Virus

As we’ve seen, the sickness can bring people back from the dead and cause them to behave in an extremely violent and erratic manner. Vocalizations seem to be brought down to nothing more than simple sentences or complete silence. Former personality traits are lost and loyalty/emotional memory seems to fade away. Claire, Sayid, and the science team were all killed or “snapped out of it” eventually, but what if they hadn’t been? Perhaps a progression of the sickness would lead to them devolving into Romero-esque zombies. This correlates the writers’ constant jokes about zombies. This could also explain the extreme fear of a fairly easily preventable infection and explain why Ethan, who seemed somewhat mild-mannered in Juliet’s flashbacks, became violent and murderous after venturing out into the jungle to infiltrate the Oceanic 815 survivors. It’s also notable that the Ajira 316 passengers that supposedly killed each other had some wounds reminiscent of those that are fatal for a traditional zombie in fiction (ie: destruction of the head).

The Sickness doesn't exist

Rousseau and the other members of the science expedition were driven insane when Nadine and Montand were suddenly killed by something they as humans couldn't comprehend (Smokey). Sayid and Claire were manipulated by promises and lies. There is no true "sickness".

  • Agree - if the sickness were real, how would Sayid and Claire have gotten over it so easily?