Women get hotter when they feel a stranger's touch - especially when the person making contact is a man, a study has shown.
Scientists measured a small but significant increase in the facial temperature of female volunteers.
A two-second touch on the face and chest, described as "high-intimate locations", had a bigger effect than touching arms and palms.
Physical contact also stimulated more warmth when it came from an experimenter of the opposite sex.
The 16 young participants, with an average age of 21, thought they were having their skin colour measured with a small flashing light device.
A thermal camera was used to take temperature readings from different areas of the face.
Across all conditions, social contact was found to cause an average shift in temperature of 0.1C.
Previous research has shown that face and body temperature increases during sexual arousal.
Fear and stress is also known to raise facial temperature. In adults, stress caused by lying or performing difficult mental tasks produces increases in skin temperature on the forehead and around the eyes.
Writing in the Royal Society journal Biology Letters, the scientists led by Amanda Hahn, from the University of St Andrews in Scotland, said: "We find that tactile contact elevates facial temperature, even when touch is an incidental part of laboratory procedure.
"Whether the changes measured in this study are detectable by others is currently unknown. If such changes in facial temperature during social contact are detectable (by observers or the individual), they could act as social cues.
"Slight increases in facial skin redness are perceived as more attractive, so it may be the case that temperature changes impact perceived attractiveness, although whether or not the skin temperature changes in interactions such as those studied here lead to detectable changes in redness and attractiveness remains to be determined."
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