There is no moment where you realise you have it, but one day it's there. An invisible barrier around you that can only be breached by certain people.
As children we treat space without care or thought, wrapping ourselves around legs, tugging at hair, diving into couches, on laps or into the arms of our parents. As adults we become more reserved and adherent to social norms, one of which is to respect people's personal space.
But how do we know where that starts and finishes?
Scientists at the University College London carried out a study into personal space in 2013 and explored two types. The first, peripersonal space (PPS), was that space around the body we consider ours. The second, defensive peripersonal space (DPPS), related to how we perceived threats. The study found that the measurement for DPPS was between 20-40 centimetres from our faces.
Researchers said the more anxious someone was, the more personal space they would need.
"In more anxious individuals, the 'safety margin' is located at a further distance from the body than in less anxious individuals," they said. "This could be because these individuals perceive threatening stimuli closer to their body than they actually are."
But one of the researchers behind the study, Dr Giandomenico Iannetti, told SBS that the measurement was adjusting constantly, depending on what situation we were in. "For example, When walking in a dangerous street at night the DPPS size is likely to increase," he said.
Dr Iannetti said this constant process of assessment was why people allowed their personal space to be breached in places where they didn't feel threatened, like a crowded train or concert, but not in others.
This 2007 photo showing Britney Spears surrounded by paparazzi as she arrived at a court hearing in Los Angeles. Celebrities routinely have their personal space invaded by fans and paparazzi. (AAP) Source: AP
The four spaces
One of the earliest researchers of this topic was US anthropologist Edward Hall. He studied personal space in the 1960s and came up with the idea that there were four different types of space: public space, social space, personal space and intimate space.
According to Hall - a Missouri man who died in 2009 - "intimate space" was reserved for close friends and partners, "personal space" and extension of that, "social space" for routine social interactions and "public space" for anonymous interactions and the general public.
In his 1966 book "The Hidden Dimension," Mr Hall argued that humans' perceptions of space were formed by a set of senses we all shared but said they were changed by culture and environment.
Edward Hall's space measurements.
Cultural differences
Dr Yasmine Musharbash, an anthropologist at the University of Sydney, said different cultural groups undoubtedly considered space in different ways.
"Societies with a strongly developed idea of the individual as a bounded, unique and independent person may require much larger personal space than members of a society where members understand themselves as interconnected to a much larger extent," she said.
"If you understand yourself through your interconnectedness to others, you would express that in closeness and distance in space. Whereas if you understand yourself as bounded and separate, you would express that spatially with a larger 'spatial buffer' around you to set you apart from others."
Chilean-born academic Gregorio Billikopf, of the University of California, carried out research into cultural differences and wrote about his own experiences adjusting to the way Americans regarded personal space when he first arrived in the country.
"I remember that on several occasions I felt my personal space was being invaded and wondered how Anglo-Saxon men could stand being so close to each other," he wrote. "After all these years, I still feel uncomfortable sitting as close to other men as often dictated by chair arrangements in the US.
"I am not the exception that proves the rule. Other foreign-born immigrants from México and Iran have mentioned feeling the same way."
"After all these years, I still feel uncomfortable sitting as close to other men as often dictated by chair arrangements in the US."
In 2009, Mr Billikopf did a study of communication and interaction, and found pronounced differences across cultures and genders.
"Neither men nor women report that women invade their personal space very frequently," he wrote in the findings.
"Men are a bit less likely (in contrast to women) to feel that a woman has invaded his personal space. Also, neither men nor women report that men invade their personal space very frequently."
"Europeans/Caucasians are the most likely to notice they were touched, followed by mixed ethnicity populations and Hispanics. Native populations and Middle Easterners were the least likely to notice they were touched."
"Hispanics (followed by Europeans/Caucasians) are least likely to feel that women invade their personal space. At the other extreme, Middle Easterners (followed by Africans) are the most likely to feel women invade their personal space."
Australia: Land of wide open space
There are more than 23 million people living in Australia, with a baby born every one minute 44 seconds. The vast majority of the country’s population live in urban areas - Sydney and Melbourne among the most densely populated - and there are huge swathes of mostly empty land in the centre.
But Dr Musharbash said that growing up in wide open environments doesn't necessarily mean people need more personal space.
"I think there is an assumption here that since many mainstream Australian require what to me often seems inordinate amounts of personal space, and since Australia is a country of wide open spaces, that the two are linked, [but] that's not how I would see it," she said.
"One comparison that would lay that [idea] to rest is taking mainstream city-dwelling Australians and comparing their need for personal space with that of Warlpiri people at Yuendumu, who have much more 'wide open space', but very different notions about personal space, of which they require very little, and not very often."
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Many of the world's poor live and work in cramped conditions where space is limited, like this slum in New Delhi, India. (AAP)
