‘The second thing is, I have a condition, which is an autoimmune condition called mast cell activation syndrome, and there’s another one called mast cell disease, and there’s mastocytosis. The 53-year-old star has lost several important people in her life in recent years (Picture: Scott Kirkland/Shutterstock)What is Mast Cell Activation Syndrome? You can read more on the Mast Cell Action website here. This is not the first time Beckinsale has opened up about how mast cell disease is impacting her life. Beckinsale is not the only celebrity to speak about having mast cell activation syndrome in recent months.