Ecto-Acne is a strange disease causing severe physical debilitation. Symptoms of Ecto-Acne include a terrible acne which covers the whole face, and physical weakness that could lead to death.
Later, Vlad once again suffers a case of Ecto-Acne. He infects Sam and Tucker with it as well, forcing Danny to find a cure.
Jack Fenton (alternate timeline)
In the alternate timeline in 'Masters of All Time," Jack is caught in the blast of his prototype portal instead of Vlad, getting infected with Ecto-Acne as well as gaining the ghost powers that Vlad has in the present timeline.
The only known cure for Ecto-Acne is ecto-purifier. It is revealed in "Masters of All Time" that Vlad caught his first case of Ecto-Acne due to Jack using diet cola, instead of ecto-purifier, in his prototype ghost portal. Ecto-Acne can wear off on its own as well, though this process can take years.