Pon Farr

Pon farr is a neuro-physiological condition in Vulcans from the Star Trek continuum. Every seven years, adult Vulcans experience an overwhelming and irresistible urge to take a mate &mdash; failure to do so could result in death. It is considered an intensely private condition that they rarely speak of with anyone outside of Vulcan society.

If a Vulcan suffering from it mind melds with someone, that someone develops it too, regardless of species.

Pon farr can be used by Sues to justify a relationship with a Vulcan. If done badly (for example, the Vulcan being open about their condition), it is a charge.

More about the pon farr at Memory-Alpha.