A simple sniffing test could determine if children have autism even before they are able to speak, researchers say.

People spend longer smelling pleasant aromas such as flowers than sour smells such as rotten food.

But researchers in Israel found during a recent trial that children with autism generated an “inappropriate” sniff, spending the same amount of time smelling each opposing aroma.

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The results, published in the Current Biology journal, showed that the more severe the symptoms of autism, the longer the children inhaled the unpleasant smells.

Researchers believe it could provide a crucial indication for autism in non-verbal children, who are usually diagnosed from the age of two, and help them to receive early behavioural interventions.

“In future, if these initial findings are confirmed and fully understood, differences relating to processing smell may offer an additional tool in diagnosing autism,” Dr Judith Brown, from the UK’s National Autistic Society, said.

Autism is a lifelong developmental disability affecting how people communicate and interact with other people.

The researchers said a sense of smell had a role in social interaction, which could explain its link with autism.

One of the researchers, PhD student Liron Rozenkrantz, told the BBC it could be a useful test from an early age.

“But before we can use it as a diagnostic test, we need to know at what age children start to develop a sniff response in the general population,” she said.

“I think what we have is an interesting place to start, but we do have a way to go.”