Up until now, researchers thought the area between organs and tissues in our body was largely solid, comprised of structural supportive proteins known as collagen, as well as stretchier elastin connective proteins. In a recently published 2018 study, scientists observed a network of fluid-filled spaces surrounded by connective tissue that fills the spaces between our organs, surrounding and potentially protecting our insides throughout the body. They define this network as a new organ, the interstitium, which they say could be the largest organ in the human body. Understanding this network as an organ could help us understand how diseases like cancer spread and it help explain what healing techniques like acupuncture are tapping into.

The new understanding of the interstitium seems to have big implications for our immune system. While white blood cells do not appear in interstitial spaces in normal tissues, evidence suggests they travel through the interstitium during an immune response when foreign material is detected. The pockets of the interstitium are supported and organized by a collagen lattice and are compressible, meaning the interstitium might also function as a shock-absorber for the organs.

The scientists who conducted this study, propose that our concept of human anatomy be officially revised to show that rather than being densely-packed barrier-like walls of collagen, spaces around organs and fascia are fluid-filled interstitial spaces. Additional research in the months and years to come, could lead us to a better understanding of why skin wrinkles as we age, why limbs get stiff, and how inflammatory diseases spread. It may also explain why cancers that spread into the space between organs are more likely to show up in other parts of the body.

In the coming years, more research will be done on the interstitium to determine whether or not we can call it an organ, and how it can change our understanding of the human body, disease, and healing.