A new lipstick has gone on sale that shows when women are in the mood for sex.

The lip product changes from clear to deep crimson as the wearer feels more and more frisky. It works by reacting with a woman’s body chemistry.

Each $18.50 tube comes with a color chart so men can figure out how aroused their partner is feeling.

The Mood Swing Emotionally Activated Lip Gloss was invented in California by Too Faced makeup brand.

"The colors change depending on your emotional state,” a spokesperson from Too Faced told The Sun.

Celebrity fans include singer Katy Perry, who is engaged to funnyman Russell Brand.

"This is the ultimate date ice-breaker,” dating expert Lorraine Adams said.

"But using it every day could get embarrassing. Would you really want the man next to you on the bus to know if you're turned on?" Adams said.