The "best friends don't hug" theory is based on similar reasoning and suggests that the more you hug your pals, the shallower your friendship. A stock photo of two female friends smiling and hugging.

Two best friends who captured the hearts of millions after they went viral last year are now featured in a clothing campaign to help raise funds for charity.

Two canine best friends from Sudbury in Ontario, Canada, who can't stop hugging each other have melted the internet's heart. A video of the dogs hugging has been viewed more than 23 million times.