DAO Enzyme (Formerly Histamine Digest) | 90 Capsules | Seeking HealthDAO Enzyme 90 Capsules by Seeking Health. Histamine is known as a biogenic amine, an organic nitrogen compound, involved in certain immune responses and found in mast cells. It may be involved in regulating healthy function in the GI tract as well as the nervous system. Histamine also plays an important role in triggering the body's normal inflammatory response. An excess of histamine can be problematic, however, leading to histamine sensitivity