Inflammation has been linked to uncontrollable temper, raising the prospect of treating anger with common drugs such as aspirin.
Markers of systemic inflammation, caused by an amplified immune response, are associated with a psychiatric condition called "intermittent explosive disorder", or IED, say scientists.
In layman's language, IED can be translated as having a very short fuse.
Sufferers are impulsive, hostile, and prone to recurrent aggressive outbursts of anger. Road rage is said to be a vivid example of the symptoms.
Researchers in the US found that people diagnosed with IED had higher markers of inflammation in the blood than those with cooler heads and average tempers.
Levels of one, C-reactive protein (CRP), were on average twice as high in "explosive" individuals.
Both CRP and another marker, the signalling molecule interleukin-6 (IL-6) were especially present in people with the worst records of aggressive behaviour.
"These two markers consistently correlate with aggression and impulsivity but not with other psychiatric problems," said lead scientist Professor Emil Coccaro, from the University of Chicago. "We don't yet know if the inflammation triggers aggression or aggressive feelings set off inflammation, but it's a powerful indication that the two are biologically connected, and a damaging combination."
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The research raises the possibility that anti-inflammatory drugs such as aspirin might help calm down people with hot tempers.
IED outbursts are characteristically disproportionate displays of anger in response to provocation that would not normally trigger such an extreme reaction.
The problem may be dismissed as simple "bad behaviour" but goes beyond that, Prof Coccaro pointed out.
"It has strong genetic and biomedical underpinnings," he said. "This is a serious mental health condition that can and should be treated."
Not only are the lives of sufferers disrupted, but also those of their family, friends and colleagues, said the researchers, whose findings are published in the journal JAMA Psychiatry.
IED raises the risk of other forms of mental illness, including depression, anxiety, and alcohol or drug abuse, they added. People with IED are also more likely to develop a host of physical health problems, including heart disease, high blood pressure, stroke, diabetes, arthritis, ulcers and headaches.
A study led by Prof Coccaro in 2006 found that the disorder affects up to 5% of adults. Typically, the first episodes of IED rage occur in adolescence, at about age 13 for boys and 19 for girls.
The two biomarkers studied have previously been linked to impulsive and aggressive behaviour in humans, cats and mice.
CRP is produced by the liver in response to an infection or injury, and helps the immune system to target dead or damaged cells.
IL-6, secreted by white blood cells, plays a role in stimulating immune responses and increases production of CRP.
The scientists measured CRP and IL-6 levels in the blood of 197 physically healthy volunteers. Of the group, 69 had been diagnosed with IED and 61 with non-aggressive psychiatric disorders, while 67 had no mental problems.
Each of the two markers independently correlated with aggression, suggesting separate associations.
Currently available treatments for IED only bring the disorder under control in half the patients treated, said the researchers. The new findings pointed to the possibility of anti-inflammatory drugs - maybe even aspirin - making a difference.
"Medications that reduce inflammation may also drive down aggression," said Prof Coccaro.