During a recent trip to Peru, my friend and I sampled the local delicacy: guinea pig. I was about to share this fact with my network of friends on Facebook (including adding a photograph of my friend with the little creature's leg sticking out of her mouth), but decided against it, thinking that it might be too horrific for my animal-loving friends.

I am not the only one who thinks twice before posting particular kinds of photographs or status messages. As a social anthropologist and user of Facebook, I have been studying Facebook habits for more than two years. During interviews and focus groups conducted with the help of Sue Hessey and Mary Lumkin from communications corporation BT, I found that Facebook users frown upon certain kinds of posting and tend to dislike ones that are "bitchy" or "negative".

I suggest that there is not unregulated social chaos on Facebook because profiles act as proxies for the people they represent. A proxy is like a deputy that has authorisation to act on the person's behalf.

As surprising as it may be to some readers, Facebook users are more circumspect about their posts than is often reported. This is at odds with neuroscientist Baroness Greenfield's argument that users post anything and everything with no regard for how it will appear. Greenfield quoted one user saying that they had 900 friends, and another saying that the fact "that you can't see or hear other people makes it easier to reveal yourself in a way that you may not be comfortable with. You become less conscious of the individuals involved (including yourself), less inhibited, less embarrassed and less concerned about how you will be evaluated."

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This seems to be borne out by some cases, as in the recent distressing example of a female Israeli soldier who posted photographs of herself with blindfolded Palestinian prisoners. The 26-year-old Eden Aberjil was surprised when she was threatened after the postings. This case and others seem to reinforce the view that those who use Facebook have lost the distinction between what is and what is not socially acceptable behaviour. Such incidents seem to confirm our worst fears that online social networking is distorting our social interactions.

However, the view that Facebook users are significantly deviating from the behaviours they exhibit during face-to-face interactions is not borne out by my findings, nor by research in Trinidad carried out by Daniel Miller, professor of materials culture at University College London. He told me: "When social scientists first claimed that the internet represented a reversal in the decline in community, I was quite sceptical. But this new research suggests that Facebook represents a genuine expansion in sustained social relationships." Miller recently launched an MSc in digital anthropology that explores the cross-cultural use of technologies such as Facebook.

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To understand why social chaos does not reign on Facebook, it is useful to introduce the concept of "face". Face is about social performance, honour and humiliation, how a person behaves when in the company of others, and is connected to norms of politeness and reputation. It is about how we attempt to manage others' opinions of us. The American sociologist Erving Goffman thought face was fundamental to how people interact with each other.

Computer-based interaction is often viewed negatively, but among young people, social networking is a very valued form of social interaction. As British academic Rob Clowes, based at the Philosophy of Language Institute in Lisbon, explains: "For young people, social networking is a way of overcoming their enforced separation. A very important reason why young people use the technology in Britain and America is because many are housebound and (the) unsupervised play of the past has disappeared. This is a space they are trying to make their own."

While social networking may provide relief for young people, it may also bring problems. A young person's sense of face is often less inhibited than that of an adult in their twenties or forties. This age-related difference in online behaviour led Eric Schmidt, chief executive officer of Google, to suggest that young people will have to change their identities because they do not understand the consequences of having too much personal information online. This view fits with issues of face. Depending on age, ethnicity, class and sexuality, individuals will post different kinds of information depending on their socially acceptable face. The type of posting depends on your face offline; hence for the Israeli soldier, it was not at odds with her face to post pictures of Palestinian prisoners because in her view this was her job and they were her prisoners.

Users of Facebook act in ways that they rarely do on other websites. First, users tend to use their real names (none of my interviewee cohort used a false name). This is quite a coup for a site as it is more common for people to use pseudonyms or usernames when logging on to public sites.

I asked Ben Light, professor of digital media at the University of Salford, whether users use their real names on sites such as Gaydar, a popular gay dating site. "On Gaydar, people take mixed approaches," he says. "Very few people put their full name - I can literally count them on one hand after 10 years of being in the space. Some mix a first name and other things, for example 'John2010' or 'southmancs'." But it is not only gay dating sites where users disguise their real names. Just take a look at the comment sections of newspaper sites: real names are rarely used.

Second, a self-portrait (profile picture) can be added to users' pages and, third, while some users have friends they have not met face to face, the bulk of friendships on Facebook are built out of face-to-face encounters. Because users are broadcasting as themselves among their group of associates, these factors affect the type of postings users make.

While commentators rightly criticise Facebook's privacy settings, in our study it was preferred to sites such as MySpace because there is a sense of control over who can view page information. Individual users operate different types of privacy settings. Therefore, what appears on a page is there as a result of decisions taken by those on your network.

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One of my interview participants explains: "I make sure I would never post anything on Facebook that I wouldn't want any of those 300 people to see. I make sure my privacy settings are set up correctly as well, so that only my friends can see my profile. Only my friends can see my pictures and only my friends can see the wall (a space where messages can be left for the user)."

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Users maintain face, or create the kind of face they would like to project, by manipulating the information they present about themselves on the screen.

Knowing what to share can be confusing for users of Facebook who centralise the complex array of social relationships in their lives. Therefore, in social networking, the rules of social interaction appear more relaxed. This is because users have to accommodate a wide range of social relationships in one place, rather than because they have lost the capacity to distinguish between (and behave appropriately for) different categories of people. Facebook posts are often banal because so much self-censorship actually takes place.

It is true that face-to-face interactions have a valuable and specific kind of quality, but people have always interacted and expressed their sociality in a multitude of ways, even before the web.

The law is particularly revealing in this respect. It is legally possible to marry with one party not physically present - this is called "proxy marriage". A famous example is the marriage of Napoleon to the Duchess of Parma in 1810; it is still allowed in some parts of the world, including California.

In a proxy scenario, an agent stands in for the person. That agent can be a person or a thing. A signature is a good example. Signatures act as a mark of the person when confirming identity.

The view that Facebook increasingly is acting as a proxy agent for people is driven home by recent cases in Australia and New Zealand. In 2009, an Australian couple who had missed payments on a significant loan could not be reached. Lawyer Mark McCormack persuaded a judge to allow him to issue legal papers to them through Facebook.

A similar situation occurred in New Zealand - a judge in Wellington allowed lawyers to issue papers via the social-networking site to a man who was recorded as having no known whereabouts.

These cases may seem bizarre, particularly when you consider an authoritative legal system of courts and judges using Facebook as a means to co-opt individuals, but a Facebook profile page carries some authority with it. Even with the privacy settings in place for users, Facebook is impressive because it has reset the rules for how people socialise with each other on the web. There is nothing wrong with being more reflective about whether one's photo of a roasted guinea pig might upset a few friends.

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