The evidence for the psychological benefits of animals is surprisingly weak

To see a man's face light up as he strokes a dog, to hear a child's laughter as her hamster tickles her skin, it just seems obvious that animals are good for our state of mind. Let's hope so because not only do millions of us own pets, but also animals are being used therapeutically in an increasing number of contexts, from residential care homes to airports, prisons, hospitals, schools and universities. Unfortunately, as detailed by psychologist Molly Crossman in her new review in the Journal of Clinical Psychology, the research literature has simply not kept pace with the widespread embrace of animal contact as a form of therapy in itself, or as a therapy adjunct. In short, we don't know whether animal contact is psychologically beneficial, and if it is, we have no idea how.

After several decades of animal-human interaction research, Crossman explains that the evidence is mixed: some studies have found benefits, others have not. And the research has tended to be of poor quality. In relation to animal-based therapy or animal-assisted therapy, for example, those studies showing benefits have usually only looked over short-term outcomes; they've not compared the generalisability of effects from one animal to another; and they've typically had no control condition, so there's no way of knowing if the apparent positive outcomes are simply due to the passage of time, or to any kind of sociable or pleasurable activity.

Another issue is that, for obvious reasons, animal-based therapy always requires the presence of a human handler, but existing studies have always failed to account for the effect of this person. This means it's possible that any benefits are solely or partly down to the friendliness and company of the handler, as opposed to the animal.

Similarly most research on the benefits of pet ownership (as opposed to animal therapy) has been observational, rather than involving any experimental allocation of pets to some participants, with other participants placed in a no-pet control condition. Again, this makes it difficult to source any apparent benefits to animal companionship per se. "There is not yet sufficient evidence to conclude that companion animal ownership conveys benefits for human health," Crossman writes.

Even if we assume that the apparent psychological benefits of animals are real, Crossman also explains that there has been virtually no research into the mechanisms. She identifies several possibilities, all of which need testing, including: the simple pleasure of the interaction; the passing of positive emotions from animal to human; feeling that the animal is providing unconditional love; and the benefits of tactile contact. There is also likely to be a large placebo effect.

Finding out how and why animal contact is psychological beneficial and for whom would help to maximise the positive impact of using animals for therapeutic reasons. Crossman points out that the idea of there being positive emotional contagion from animal to human also reminds us that it's important to consider the effect of animal therapy on animals, and not to sacrifice their welfare in the process of helping people.

Some may wonder whether it matters that there is such a dearth of quality research in this field. As Crossman says, many people just feel they "know" that animal contact is beneficial and "they're often sceptical of the need for empirical evidence." But the wider psychotherapy literature teaches us that there are dangers in assuming interventions are always going to be helpful – animal therapy or ownership might not work for everyone, and in some cases it could even be detrimental. For instance, the responsibility of a pet might backfire for someone who is struggling to cope with stress.

"Researchers and practitioners have called for methodological improvements and advancements [in human-animal interaction research] for nearly half a century, but those calls remain largely unanswered," Crossman writes. "At this point, the clearest conclusion in the field is that we cannot yet draw clear conclusions."

Further reading

—Effects of Interactions With Animals On Human Psychological Distress