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.