Deadpool's primary power is an accelerated healing factor, depicted by various writers with differing levels of efficiency. Artificially endowed by the Weapon X program, this enables him to regenerate any destroyed tissue at a super-human rate as well as making him immune to all known diseases. An unanticipated side effect was an acceleration of the cancerous tumors he was suffering from at the time, causing them to quickly spread across his entire body. Because of this, his healing factor super charged his cancer, resulting in massive scar tissue causing his appearance to be severely disfigured.
Deadpool's brain cells are similarly affected, with dying brain cells being rejuvenated at a super accelerated rate. This allows Deadpool to recover from any and all head wounds, and it renders him nearly invulnerable to psychic and telepathic powers, as the altered or damaged brain cells quickly regenerate to their original state. It is also the cause of his psychosis and mental instability. It is sometimes implied that his healing factor merely bolstered and exacerbated an underlying mental issue, as a young Wade Wilson was shown as a withdrawn, disturbed young kid caught in his zany daydreams and, upon losing his healing factor, Deadpool didn't regain his sanity. Deadpool's healing factor is strong enough that he has previously survived complete incineration and decapitation more than once, though his head had to be reunited with his body to heal the wound. Unlike Wolverine’s natural healing factor, Deadpool’s is mentally driven. Similar to Wolverine, his healing factor also affects his physical attributes by increasing them to superhuman levels.