Australian scientists have found the secret to why our skin goes wrinkly but doesn't dissolve in the bath.
Myfanwy Evans of the Australian National University in Canberra, and colleagues, report their findings today in the Journal of the Royal Society Interface.
"When we are in the bath and we have been there for a while the stratum corneum [outer] layer of our skin expands," says Evans. "This causes wrinkles and means our finger prints will be enlarged also."
Evans says previously researchers had proposed that the stratum corneum had a structure that was capable of expanding as it absorbed water. But they couldn't explain why the skin didn't fall apart as it expanded.
She and colleagues have been modelling structures like the stratum corneum on computer, and have identified the special feature of skin that helps explain why it stays intact in the bath.
"We're coming at it from a completely geometric point of view in order to try and explain some of the phenomena that are seen in skin," says Evans, who has just completed a PhD under the supervision of Professor Stephen Hyde.
"Our model provides an explanation as to why the skin maintains its structural rigidity and expansion in water, which was something that was never quite able to be explained," says Evans.
Evans says the stratum corneum is made up of helical fibres of keratin that are woven together in a three-dimensional pattern.
The researchers found the particular weave of the keratin enables it to act like a sponge, staying robust while absorbing water.
The helical fibres also straighten out, allowing the material to expand and increase the volume of water it can hold, says Evans.
But the key point is that as the material expands, all of the contacts between each of the fibres are maintained.
"Contact between fibres are what gives the material structural stability," says Evans.
"In this expansion all of those inter-fibre contacts are maintained so the material stays as a rigid material."
Hence the remarkable properties of skin while we soak in the bath - as long as we don't stay too long. But Evans says after 24 hours of contact with water, irreversible damage can occur to the skin.
She says the new understanding will make it easier for scientists to make materials that have this same property as skin.