The merest interaction with a member of the opposite sex can bring a glow to a woman's face, according to a new study.
Researchers at the University of St Andrews found even non-sexual contact with men caused a noticeable rise in the temperature of a woman's face.
The team used thermal imaging to detect changes in heterosexual women during their meetings with other people.
They found that even without noticing, a woman's face would heat up in the company of the opposite sex.
The team behind the discovery said the findings could be used in the development of thermal imaging to monitor levels of stress and emotion in future, for example in lie detection tests.
Lead author of the study, Amanda Hahn, said researchers measured skin temperature on a woman's hand, arm, face and chest when they interacted with men.
They found the most dramatic increase occurred in a woman's face, where temperatures rose by an entire degree in some cases.
She said: "This thermal change was in response to simple social interaction, without any experimental change to emotion or arousal. Indeed our participants did not report feeling embarrassment or discomfort during the interaction."
The study, published later this month in Biology Letters, shows that gender alone influenced the reaction of women, who showed very little response to interaction with other women.
Prof David Perrett, who was also part of the research team, added, "We are only just beginning to understand the potential uses of thermal imaging in medicine and it can be very useful in areas of national security, where changes in skin temperature can be gauged as part of lie detection tests."
The research team's next goal is to work out whether or not these physiological changes are detected by others and whether they affect social interactions.