Fainting could be triggered by a combination of genetic and environmental factors, a study involving twins has found.
University of Melbourne and Austin Health research found identical twins, who have identical sets of genes, were almost twice as likely to faint as non-identical twins.
The study examined 51 sets of twins aged between nine and 69 with a history of fainting.
Fainting can be caused by the body's reaction to typical triggers, such as injury or the sight of blood, or environmental factors like heat.
The study found identical twins fainted more than non-identical twins and were also more likely to report environmental triggers, such as heat, as the cause.
Identical twins were also much more likely to both experience fainting caused by typical triggers, than non-identical twins.
Study author Professor Sam Berkovic from the University of Melbourne found that fainting was probably inherited from more than one gene.
"Our results suggest that while fainting appears to have a strong genetic component, there may be multiple genes and multiple environmental factors that influence the phenomenon," Prof Berkovic, who is based at Austin Health, said.
Dr Berkovic said fainting was poorly understood and more information about the genetic and environmental triggers could improve the treatment for frequent sufferers.
About 25 per cent of the population faint at some point in their life.
The research was published in the international journal Neurology.