Saddle Rash (2002)

S2E28 Allergy Time

The Skipper starts to sneeze and itch whenever he's near Gilligan, and soon, the rest of the Castaways experience similar symptoms. Concerned, the Professor creates a vaccine, but it fails to alleviate their discomfort. Eventually, they discover that the culprit behind the allergies is the papaya oil in Gilligan's hair tonic, which is affecting everyone.