It doesn’t take a scientist to know that pets make humans feel good; anyone who’s ever stroked a dog’s fur or felt a cat’s thrumming purr knows this. Science can, however, tell us how and why pets can be therapeutic. Just 15 minutes bonding with an animal sets off a chemical chain reaction in the brain, lowering levels of the fight-or-flight hormone cortisol and increasing production of the feel-good hormone serotonin. The result: heart rate, blood pressure and stress levels immediately drop. Over the long term, pet and human interactions can lower cholesterol levels, fight depression and may even help protect against heart disease and stroke. This is why pets for the elderly can be so beneficial.