Our families smell - and it's part of the natural mechanism to deter incest, say scientists.

Previous studies have suggested that smell is important in family relationships -mothers and babies learn each other's smell soon after birth.

But researchers in the United States looked at 25 families with at least two children aged six to 15 to see what part smell played in other family relationships.

It gave all family members T-shirts which they were asked to sleep in for three nights.



Preferring a smell is not a precursor to mating.

Professor Tim Jacob, Cardiff School of Biosciences

They were only allowed to wash with odourless soap they were given.

Each morning the T-shirts had to be sealed in plastic bags.

The volunteers were then asked to sniff two T-shirts - one worn by a family member and one by an unknown and unrelated person.

Fathers and mothers were asked if they could identify their children's scent, and children if they could detect the scent of their parents or siblings.

Everyone who took part in the study was also asked which smell they preferred.

Strange scents

Mothers and fathers recognised the smell of their children, though mothers tended to be more accurate.

But neither could distinguish between their children.

Children aged five to eight did not recognise their mother's smell, while older children aged nine to 15 did.

But it was the answers to which smells they preferred which surprised researchers.

The smell of strangers was deemed to be far preferable to the smell of close relatives.

Mothers particularly disliked their children's smells, while children hated their father's scent.

New Scientist magazine, which reported the research, said: "She thinks that disliking the smell of close family might be part of the mechanism that helps prevent incest.

"Particularly notable is the fact that opposite-sex siblings disliked each other's smells, while same sex siblings did not."

Immune link

But Tim Jacob, a professor of physiology at the Cardiff School of Biosciences who specialises in smell, told BBC News Online the US research was "a very over-interpreted piece of work using a very small sample".

He added: "Smell preferences are well known to be linked to the immune system.

"We prefer the smell of people with different immunotypes to ourselves - this improves the immune competence of our offspring."

But he added: "Preferring a smell is not a precursor to mating. Being attracted to someone's smell is one of many complex cues to forming a closer relationship.

"Smell preferences are part of an evolutionary mechanism that concerns mate choice - in humans, finding that one person in a million."