In psychology and health research, saliva samples are often used to measure what's happening in your body without needing a blood draw. By collecting a small amount of spit—usually by drooling into a tube or using a cotton swab—researchers can look at things like cortisol (a hormone related to stress), cytokines (which are involved in inflammation), and other biological markers. These substances give insight into how your body is reacting to stress, illness, or different environments. Saliva is easy to collect, non-invasive, and safe, which makes it perfect for studies that want to connect physical health with mental health or behavior.