Honeymoon long over? Hang in there.

A new US study shows those prickly disagreements that can mark the early and middle years of marriage mellow with age as conflicts give way to humour and acceptance.

Researchers analysed videotaped conversations between 87 middle-aged and older husbands and wives who had been married for 15 to 35 years, and tracked their emotional interactions over the course of 13 years.

They found that as couples aged, they showed more humour and tenderness towards another.

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Overall, the findings, just published in the journal Emotion, showed an increase in such positive behaviours as humour and affection and a decrease in negative behaviours such as defensiveness and criticism.

The results challenge long-held theories that emotions flatten or deteriorate in old age and point instead to an emotionally positive trajectory for long-term married couples.

"Our findings shed light on one of the great paradoxes of late life," said study senior author Professor Robert Levenson, at the University of California at Berkeley.

"Despite experiencing the loss of friends and family, older people in stable marriages are relatively happy and experience low rates of depression and anxiety.

"Marriage has been good for their mental health."

Consistent with previous findings, the 25-year longitudinal study found that wives were more emotionally expressive than their husbands, and as they grew older they tended toward more domineering behaviour and less affection.

But generally, across all the study's age and gender cohorts, negative behaviours decreased with age.

So cute I could crush it

Feel the urge to hurt this puppy? You may be experiencing
Feel the urge to hurt this puppy? You may be experiencing "cute aggression". Photo / 123RF

Have you ever looked at a puppy and had the urge to squeeze or even bite it?

Or felt compelled to pinch a baby's cheeks, albeit without a desire to harm it?

If you answered yes to either question, you've experienced a phenomenon called cute aggression - and you're far from alone.

Until now, research exploring how and why cute aggression occurs has been the domain of behavioural psychology.

But more recently, researchers have taken formal study of the phenomenon a few steps further.

In a new study, Katherine Stavropoulos, an assistant professor at the University of California, Riverside, used electrophysiology to evaluate surface-level electrical activity that arose from neurons firing in people's brains.

By studying that activity, she gauged neural responses to a range of external stimuli in a group of 54 adults.

Based on this, she found direct evidence of both the brain's reward system and emotion system being involved in the phenomenon.

"There was an especially strong correlation between ratings of cute aggression experienced toward cute animals and the reward response in the brain toward cute animals," she said.

"This is an exciting finding, as it confirms our original hypothesis that the reward system is involved in people's experiences of cute aggression."

She also found the relationship between how cute something was and how much cute aggression someone experienced toward it appeared to be tied to how overwhelmed that person was feeling at the time.

"Essentially, for people who tend to experience the feeling of 'not being able to take how cute something is,' cute aggression happens," Stavropoulos said.

"Our study seems to underscore the idea that cute aggression is the brain's way of 'bringing us back down' by mediating our feelings of being overwhelmed."

The deadly bug on everyone's skin

"Staphlococcus epidermidis is a deadly pathogen in plain sight," says Professor Sam Sheppard, of the University of Bath's Milner Centre for Evolution. Photo / University of Bath

Forget MRSA and E. coli.

There's another bacterium that is becoming increasingly dangerous due to antibiotic resistance - and it's present on the skin of every person on the planet.

A close relative of MRSA, Staphylococcus epidermidis, is a major cause of life-threatening infections after surgery, but it is often overlooked by clinicians and scientists because it is so abundant.

Researchers from the University of Bath in the UK warn that the threat posed by this organism should be taken more seriously and use extra precautions for those at higher risk of infection who are due to undergo surgery.

They have identified a set of 61 genes that allow this normally harmless skin bacterium to cause life-threatening illness.

They hope that by understanding why some strains of S. epidermidis cause disease in certain circumstances, they could in the future identify which patients are most at risk of infection before undergoing surgery.

They took samples from patients who suffered infections following hip or knee joint replacement and fracture fixation operations and compared them with swab samples from the skin of healthy volunteers.

They compared the genetic variation in the whole genomes of bacteria found in samples from diseased and healthy individuals.

From this they identified 61 genes in the disease-causing bacteria that weren't present in most of the healthy samples.

Surprisingly however, there was a small number of healthy individuals who were found to be carrying the more deadly form of the bacteria without knowing it.

The disease-causing genes were found to help the bacterium grow in the bloodstream, avoid the host's immune response, make the cell surface sticky so that the organisms can form biofilms and make the bug resistant to antibiotics.

"Staphlococcus epidermidis is a deadly pathogen in plain sight," said Professor Sam Sheppard, of the university's Milner Centre for Evolution.

"It's always been ignored clinically because it's frequently been assumed that it was a contaminant in lab samples or it was simply accepted as a known risk of surgery.

"Post-surgical infections can be incredibly serious and can be fatal. Infection accounts for almost a third of deaths in the UK so I believe we should be doing more to reduce the risk if we possibly can.

"If we can identify who is most at risk of infection, we can target those patients with extra hygiene precautions before they undergo surgery."