Artificial skin that could be used to replace animals in tests of drugs and cosmetics has been grown in the laboratory for the first time.
Scientists in the UK and US produced one centimetre-wide fragments of epidermis - the outermost skin layer - from stem cells with the same properties as real skin.
The epidermis forms a protective barrier between the body and external environment, preventing water from escaping while keeping out microbes and toxins.
Until now, tissue engineers have been unable to grow an outer skin layer with the functional barrier needed for drug testing.
In future, lab-grown skin could be used for testing medicinal lotions and creams or cosmetics without causing suffering to animals, scientists believe.
It could also provide a model for investigating skin conditions such as eczema.
Testing cosmetics on animals is banned in the UK and from last month it has been illegal to import or sell products containing ingredients tested on animals in the European Union.
However, cosmetics testing continues in other parts of the world, including China and the US.
Dr Dusko Ilic, who led the British team from King's College London, said: "Our new method can be used to grow much greater quantities of lab-grown human epidermal equivalents, and thus could be scaled up for commercial testing of drugs and cosmetics.
"Human epidermal equivalents representing different types of skin could also be grown, depending on the source of the stem cells used, and could thus be tailored to study a range of skin conditions and sensitivities in different populations."
The artificial skin was derived from induced pluripotent stem (iPS) cells created by genetically altering donated fibroblast cells from adult connective tissue.
IPS cells have the same properties as embryonic stem cells, including the ability to develop into virtually any kind of tissue in the body.
A step-by-step process in the laboratory transformed the iPS cells into keratinocytes - the dominant cell type in the outermost layer of the skin - and then pieces of actual skin.
The scientists called their constructs "3D epidermal equivalents". Tests showed no significant differences in structure or function between the artificial patches and real human skin.
Dr Ilic added: "When you produce a new cream you need to know how much of it goes through the skin, because if there's too much it can cause damage.
"If you imagine the skin as a three or four-storey building with a roof on top, other people have made the roof but their roofs are always leaking. They could not get their tiles together. We are the first to achieve this.
"Our approach is cost-effective, because once you have the iPS cells you can grow an infinite number."
He said it would be a simple matter to create skin patches measuring 10 square centimetres rather than one, but pointed out that small fragments might be more useful.
The research is published in the latest edition of the journal Stem Cell Reports.
As well as testing drugs and cosmetics, the artificial skin could also be used to study eczema and other conditions that involve the skin failing to provide an effective barrier.
US co-author Dr Theodora Mauro, from San Francisco Veteran Affairs Medical Centre, said: "The ability to obtain an unlimited number of genetically identical units can be used to study a range of conditions where the skin's barrier is defective due to mutations in genes involved in skin barrier formation, such as ichthyosis (dry, flaky skin) or atopic dermatitis (eczema).
"We can use this model to study how the skin barrier develops normally, how the barrier is impaired in different diseases and how we can stimulate its repair and recovery."
Dr Katy Taylor, head of science at the British Union for the Abolition of Vivisection (BUAV) said: " We welcome this new technique as a significant humane development to replacing cruel animal tests."