Benjamin Franklin famously said that guests, like fish, begin to smell after three days. Many of us are inclined to agree. I recently struggled to share my space and resources with a houseguest. I wanted to be hospitable, yet I experienced an unexpectedly inhospitable reaction to my mackerel-like guest (herein known as “Mack”). The dissonance was intense. What was up with that? Fortunately, my psychology arsenal includes tools from the psychology subdiscipline of environmental psychology. It is there we find theories and research on human territoriality that explain the trouble with houseguests (at least some of it!).

At the heart of the matter is that houseguests temporarily set up their personal shop in another’s primary territory. In contrast to secondary territories (like workplaces) and public territories (like stores), this is typically a cherished, personal territory where inhabitants have a high degree of personal control over an extended period of time. This, in combination with predictable routines, norms, and roles, reduces stress and makes our homes secure, restorative environments requiring little adaptive energy.

Houseguests, then, are stressful to the extent that they disrupt our routines and usurp the high amount of control we normally enjoy in this personal territory. If their routines interfere with ours or if their presence restricts our normal uses of home spaces, stress is likely. Maybe Ben was right: a few days we can tolerate, but stress builds as visits go on. Anxiety-prone hosts, in particular, may become stressed by disruptions in their routines and loss of control over personal spaces.

Primary territories also differ from other territories because their occupants feel a sense of ownership (i.e., “This is my home and my stuff”). When guests invade our territory by roaming too freely throughout our home or touching our personal items, when they contaminate our territory by leaving their stuff around or not cleaning up after themselves, or when they create resource shortages by snarfing our food or using all the hot water, we naturally experience this as a territorial invasion and react defensively.

To some extent, these defensive reactions are instinctual, especially if a guest is not considered a member of our “tribe” with a legitimate claim to share our primary territory. We are more willing to share personal territories and resources with members of our group. That Mack, my fishy guest, was a stranger, in tow with a beloved sister, didn’t help matters.

Of course, we are not just animals but social animals. Social norms requiring politeness and hospitality usually override overt territorially defensive actions (e.g., “You have to leave my territory, NOW, or harm may come to you”). Instead, hosts typically communicate feelings of invasion through social withdrawal and short-temperedness.

Primary territories are also the most private of territories. We can control others’ access to us, which reduces stress and promotes recovery. Most of us need time at home alone or with a few trusted others to recharge before we go back into the world. This varies based on culture and individual differences. For example, introverts, like me, have high privacy needs. Mack upped his fishiness quotient by inserting himself into private conversations, intruding in private spaces (my bedroom!), and being omnipresent (in spite of the fact that he was not a Holy Mackerel). Altman’s privacy regulation theory would predict that houseguests are stressful to the extent that they create a “disconnect” between hosts’ actual and desired levels of privacy.

Of course, territoriality isn’t the whole picture. Among other things, increased household labor also makes guests “smelly” (often more of an issue for women in traditionally gendered households where they bear the brunt of cooking and cleaning). The moral of this story: if you want to stay a welcome houseguest, it probably pays to respect your host’s home as a primary territory, and to keep your visit short.