Relationships - Desire
Every adult Sim is capable of growing desire which can be translated into lust and sexual satisfaction.
Sims get a positive lust moodlet when their desire reaches at least 50% of the maximum capacity. Too much desire, which is at least 85%, will replace the positive moodlet with a negative one, from having too much desire that is not being released.
Sims with high desire are more keen on agreeing to sex and will more often decide to masturbate.
Releasing desire with sex helps to achieve more positive sexual satisfaction.
Sims mainly gain desire from positive romantic conversations. Friendly conversations have the most potential when talking to naked Sims. Any negative or mean interactions lower desire.
Exhibitionist Sims gain desire from looking at naked Sims.
Traits like Alluring or Romantic increase the amount of gained desire. Sims with the Unflirty trait gain less desire. And Sims with the Sexually Abstinent trait gain no desire.
Vampire Sims that talk to Sims on their period will gain more desire.