A new Australian study has added weight to suggestions that smartphone addiction among young people is becoming an increasing public health issue.

Smartphone addiction is affecting productivity, emotional wellbeing and relationships, a study of young Australians has found.

The Deakin University study of almost 400 undergraduate students found a third felt anxious if they were unable to regularly check their phones.

Forty per cent felt lost without it, 34 per cent lost sleep due to time spent on their devices and more than half were on their phones when they should be doing other things.

Lead researcher Dr Sharon Horwood said the findings were surprising, and added weight to suggestions problematic smartphone use is becoming an increasingly prevalent public health issue.

"There's no doubt that smartphones have changed the way we do things, and given that around 88 per cent of Australian have smartphones, we must feel as though we get something good from using them," she said.

"However, when usage becomes excessive it can result in a range of negative outcomes including low mood, reduced physical fitness, sleep deprivation and poorer academic performance."

Dr Horwood said smartphone use becomes problematic when it begins to impact on daily functioning, including productivity, relationships or physical or emotional heath.

Fear of missing out, or FoMO, is one theory for why people can become overly reliant on their phones as they feel the need to constantly stay online and connected via social media.

Another major factor is the design of the phone and apps, which are "deliberately addictive" to entice users to stay on them as long as possible.

But Facebook and Instagram were only part of the story, with the study finding the mindless checking of smartphones out of habit rather than need, and entertainment use, such as watching videos or web browsing, was more closely linked to problematic use than using social media.

Dr Horwood said personality was a strong predictor of problematic use, with the study identifying participants with higher levels of neuroticism and lower levels of conscientiousness.

"One explanation could be that individuals high in neuroticism tend to rely on their smartphones to obtain social and emotional reassurance from relationships," she said.

"Whereas conscientious people are characterised by a willingness to delay short-term gratification in order to achieve other goals in work, education, health and wellbeing.

"The thing to keep in mind is that broad personality traits such as neuroticism and conscientiousness influence the way we think and see the world generally, not just in relation to how we use technology."

The study was published in the journal Computers in Human Behavior.