A long-standing debate has developed around the ultimate source of emotions. The James-Lange theory proposes that an emotion starts with a physical reaction in the body, and then filters up to the head where we put a word to the response, and recognise it as an emotion. The Canon-Bard theory proposes that we first feel the emotion in our heads, and then our body reacts (with increased heart rate, etc.).

Candace Pert's answer to this debate is that an emotion happens simultaneously in the head and body. In Pert's theory emotions are the peptides. It is through the peptides (and other ligands) that emotions can originate both in the head, influencing the body, and originate in the body, influencing the head.

She says our every move, function and thought is influenced by our emotions because they are these peptides (or information substances) which bring the messages to all our body cells. She is suggesting our emotions are molecules and exist in real, concrete, biological form.

This would explain why and how our health is affected by emotions. If these peptides are our emotions, then they continually come into contact with our immune system, endocrine system, nervous system, etc. Depending on our emotional state (happy, sad, angry, etc), different peptides are released and hence, different messages are sent throughout the body. For example, feelings of bliss and bonding are accompanied by the release of endorphins into the body's communication highway. Feelings of self-love are accompanied by a peptide called VIP (Vasoactive Intestinal Peptide). Each peptide has its own emotional tone or mood that you can experience.