They're said to be man's best friend. Now we may know why, and it's all down to those irresistible puppy dog eyes.

Scientists say when an owner looks its pet in the eye it can lead to an increase in a hormone which ignites feelings of love.

A study claims gazing causes oxytocin to spike.

One of the hormone's main jobs is to help a parent bond with their child, so it can be produced when a mother breastfeeds or looks at her baby.

Oxytocin has also been observed in both dogs and people when they take part in activities like petting and playing.

Experts think the bond between a dog and its owner probably developed after humans began domesticating dogs.

The new research, which was carried out by scientists at Azabu University in Japan and published in the journal Science, involved two experiments.

Experiment one

Researchers had the pleasant task of collecting urine from a group of dogs and their owners before and after a 30-minute interaction.

The samples showed that those who gazed at each most experienced the biggest surge of oxytocin in their urine.

Experiment two

Researchers sprayed oxytocin into a group of dogs noses and found female dogs stared longer at their owners afterwards.

The gazing also increased the owners levels of oxytocin.

Scientists who worked on the study say it highlights the benefits of gazing at your pet, instead of simply telling it what to do.

They also investigated whether oxytocin levels would increase when hand-raised wolves interacted with a known human.

But the wolves only held a gaze with the humans for a few seconds.

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