"It's not a conscious process, so we don't even realise we're doing it but it goes back to our primitive roots when we couldn't afford to make wrong decisions," she said.
Judi James, author of The Body Language Bible, agrees that it comes naturally to us and that even though we know it is not an accurate way of evaluating another person, we still do it.
"Judging other people in the first few seconds of meeting them is part of our survival response. So, although we might understand that it's a flawed and prejudiced way of evaluation, we can't stop ourselves doing it," she explained.
"Because we tend to be time-poor, we use assumption as a short-cut, meaning if you don't get it right first time you might not get another chance," she said.
James warns that while we instantly judge others, we also slip up on signals we ourselves give out, which makes us arrive at business or social events looking dour, anxious, shy or hostile, without realising it.
Expert tips on how to pass the seven-second test includes, taking a moment before meeting people to check on appearance and to breathe out gently to remove tension and calm any nerves caused by shyness or anxiety.
Pulling oneself up to full height will make one look confident and also relax muscle tension.
Image consultant Karen Gillam advices turning off one's cell phone or putting it on silent and to smile at the other person as it would instantly help to strike a rapport.
Showing interest in the other person also helps but invading their personal space does not and always use open gestures, rather than fold your arms or cross your legs.