Editing Fear (section)

====Humans====
Evidence of chemosensory alarm signals in humans has emerged slowly: Although alarm pheromones have not been physically isolated and their chemical structures have not been identified in humans so far, there is evidence for their presence. [[Androstadienone]], for example, a steroidal, endogenous odorant, is a pheromone candidate found in human sweat, axillary hair and plasma. The closely related compound [[androstenone]] is involved in communicating dominance, aggression or competition; sex hormone influences on androstenone perception in humans showed a high testosterone level related to heightened androstenone sensitivity in men, a high testosterone level related to [[unhappiness]] in response to androstenone in men, and a high estradiol level related to disliking of androstenone in women.<ref>{{cite journal | vauthors = Lübke KT, Pause BM | title = Sex-hormone dependent perception of androstenone suggests its involvement in communicating competition and aggression | journal = Physiology & Behavior | volume = 123 | pages = 136–141 | date = January 2014 | pmid = 24184511 | doi = 10.1016/j.physbeh.2013.10.016 | s2cid = 25729942 }}</ref>

A German study from 2006 showed when anxiety-induced versus exercise-induced human sweat from a dozen people was pooled and offered to seven study participants, of five able to olfactorily distinguish exercise-induced sweat from room air, three could also distinguish exercise-induced sweat from anxiety induced sweat. The [[startle reflex|acoustic startle reflex]] response to a sound when sensing anxiety sweat was larger than when sensing exercise-induced sweat, as measured by [[electromyography]] analysis of the orbital muscle, which is responsible for the eyeblink component. This showed for the first time that fear chemosignals can modulate the startle reflex in humans without emotional mediation; fear chemosignals primed the recipient's "defensive behavior" prior to the subjects' conscious attention on the acoustic startle reflex level.<ref>{{cite journal | vauthors = Prehn A, Ohrt A, Sojka B, Ferstl R, Pause BM | title = Chemosensory anxiety signals augment the startle reflex in humans | journal = Neuroscience Letters | volume = 394 | issue = 2 | pages = 127–130 | date = February 2006 | pmid = 16257486 | doi = 10.1016/j.neulet.2005.10.012 | s2cid = 23295966 }}</ref>

In analogy to the social buffering of rats and honeybees in response to chemosignals, induction of [[empathy]] by "smelling anxiety" of another person has been found in humans.<ref>{{cite journal | vauthors = Prehn-Kristensen A, Wiesner C, Bergmann TO, Wolff S, Jansen O, Mehdorn HM, Ferstl R, Pause BM | display-authors = 6 | title = Induction of empathy by the smell of anxiety | journal = PLOS ONE | volume = 4 | issue = 6 | page = e5987 | date = June 2009 | pmid = 19551135 | pmc = 2695008 | doi = 10.1371/journal.pone.0005987 | bibcode = 2009PLoSO...4.5987P | doi-access = free }}</ref>

A study from 2013 provided brain imaging evidence that human responses to fear chemosignals may be [[gender-specific]]. Researchers collected alarm-induced sweat and exercise-induced sweat from donors extracted it, pooled it and presented it to 16 unrelated people undergoing functional brain [[MRI]]. While stress-induced sweat from males produced a comparably strong emotional response in both females and males, stress-induced sweat from females produced markedly stronger arousal in women than in men. Statistical tests pinpointed this gender-specificity to the right amygdala and strongest in the superficial nuclei. Since no significant differences were found in the [[olfactory bulb]], the response to female fear-induced signals is likely based on processing the meaning, i.e. on the emotional level, rather than the strength of chemosensory cues from each gender, i.e. the perceptual level.<ref>{{cite journal | vauthors = Radulescu AR, Mujica-Parodi LR | title = Human gender differences in the perception of conspecific alarm chemosensory cues | journal = PLOS ONE | volume = 8 | issue = 7 | page = e68485 | date = Jul 2013 | pmid = 23894310 | pmc = 3722227 | doi = 10.1371/journal.pone.0068485 | bibcode = 2013PLoSO...868485R | doi-access = free }}</ref>

An [[approach–avoidance conflict|approach-avoidance task]] was set up where volunteers seeing either an angry or a happy cartoon face on a computer screen pushed away or pulled toward them a joystick as fast as possible. Volunteers smelling androstadienone, masked with clove oil scent responded faster, especially to angry faces than those smelling clove oil only, which was interpreted as androstadienone-related activation of the fear system.<ref>{{cite journal | vauthors = Frey MC, Weyers P, Pauli P, Mühlberger A | title = Androstadienone in motor reactions of men and women toward angry faces | journal = Perceptual and Motor Skills | volume = 114 | issue = 3 | pages = 807–825 | date = June 2012 | pmid = 22913022 | doi = 10.2466/07.16.22.28.PMS.114.3.807-825 | s2cid = 13194791 }}</ref> A potential mechanism of action is, that [[androstadienone]] alters the "emotional face processing". Androstadienone is known to influence the activity of the [[fusiform gyrus]] which is relevant for [[face perception|face recognition]].