There is a 2013 study on this topic which concluded that domestic cats living in multi-cat homes are not more stressed because of their living arrangements. There may be some stressed cats in the group but the added stress is not in general caused by the fact that the cats are in a multi-cat home.
“GCM [fecal glucocortoid metabolites] did not significantly vary as a function of living style (single, double or group housing); highly stressed individuals were equally likely in the three groups…”
In fact younger cats in multi-cat homes had a lower stress levels on the basis of GCM. Cats who tolerated rather than liked petting tended to have higher GCM levels i.e. were more stressed. The topic of whether domestic cats like being petted is an interesting one. Not all cats do like it and cat owners should be aware of this.
The study concluded that factors other than living in a multi-cat household play a role in creating stress such as the relationship with the people in the home and availability of resources such as food. This is a reference to the possibility of one cat bullying another over food and access to the litter tray. Also a failure to provide hiding places for timid cats can heighten stress levels in those cats.
The study was conducted because there is this grey area on how the essentially solitary domestic cat has evolved to become a rather sociable animal. There are many signs that the domestic cat does not behave like their wild cat ancestor such as mutual grooming and close, mutually supportive friendships being formed.
The study: Are cats (Felis catus) from multi-cat households more stressed? Evidence from assessment of fecal glucocorticoid metabolite analysis. Department of Medical Clinics, Faculty of Veterinary Medicine and Animal Science, University of São Paulo [link].
SOME MORE ON STRESS….