Because of their small size, domesticated house cats pose little physical danger to adult humans. However, in the USA cats inflict about 400,000 bites per year. This number represents about one in ten of all animal bites.[Many cat bites will become infected, sometimes with serious consequences such as cat-scratch disease, or, more rarely, rabies. Cats may also pose a danger to pregnant women and immunosuppressed individuals, since their feces can transmit toxoplasmosis. A large percentage of cats are infected with this parasite, with infection rates ranging from around 40 to 60% in both domestic and stray cats worldwide.
Allergic reactions to cat dander and/or cat saliva are common. Some humans who are allergic to cats—typically manifested by hay fever, asthma, or a skin rash—quickly acclimate themselves to a particular animal and live comfortably in the same house with it, while retaining an allergy to cats in general. Whether the risk of developing allergic diseases such as asthma is increased or decreased by cat ownership is uncertain. Some owners cope with this problem by taking allergy medicine, along with bathing their cats frequently, since weekly bathing will reduce the amount of dander shed by a cat. There have also been attempts to breed hypoallergenic cats, which would be less likely to provoke an allergic reaction.
As well as posing health risks, interactions with cats may improve health and reduce physical responses to stress: for example the presence of cats may moderate increased blood pressure.[ Cat ownership may also improve psychological health by providing emotional support and dispelling feelings of depression, anxiety and loneliness.[ Their ability to provide companionship and friendship are common reasons given for owning a cat.
From another point of view, cats are thought to be able to improve the general mood of their owners by alleviating negative attitudes. According to a Swiss study carried out in 2003, cats may change the overall psychological state of their owner as their company's effect appears to be comparable to that of a human partner. The researchers concluded that, while cats were not shown to promote positive moods, they do alleviate negative ones.
One study found that cat ownership is associated with a reduced risk of heart attacks and strokes at the 95% confidence interval.
Several studies have shown that cats develop affection towards their owners. However, the effect of these pets on human health is closely related to the time and effort the cat owner is able to invest in it, in terms of bonding and playing.[