Mastocytosis is a rare disorder (or disease).  Medical research articles alternate between classifying it as a "disorder" or a "disease", depending on the researcher's focus on the various forms or types of Mastocytosis.  MSC uses both classifications in an effort to be inclusive for all patients, regardless of type, form, variant or subvariant within the Mastocytosis definitions.

Mastocytosis and Mast Cell Activation Sydrome affect all systems, organs and tissues of the body.  In particular, skin, liver, spleen, lymph nodes, bones and bone marrow, lungs, gastrointestinal system, eyes and blood.  Research exists but much more needs to be done to further identify and understand the less studied effects of mast cell disorders on the heart, brain and female reproductive system.

Mastocytosis and related mast cell disorders are classified as rare, however an increased prevalence of these patients worldwide has resulted in a flurry of medical research in numerous countries.  This indicates that these disorders may not be rare, but rather have been commonly misidentified and undiagnosed. Since 2005, new theories, classifications, and adjustments to the Mastocytosis definitions have been published due to the increased numbers of patients presenting with mast cell disease and the increased research in this field.