DAO is present in your small intestine where it naturally degrades and helps to eliminate histamine in order to protect a balance in your body. Under normal, balanced conditions, DAO and histamine comfortably coexist. However, our diet has changed and we consume less DAO (liver anyone?) while more and more foods are processed and therefore fermented, meaning they contain higher amounts of histamine. The body can no longer naturally cope with the challenge causing more and more people to lack a sufficient supply of DAO. In their case, histamine goes unchecked and can create an imbalance either every day or just from time to time.