Banking blood does not provide a rich diversity of cells you find in other cell sources, like the hair follicle. The cells found in blood are also difficult to expand, less flexible and less able to divide and replicate than other types of cells. This means that it is more difficult to grow and maintain in culture, and it is also more difficult to stimulate its growth and differentiation into different types of cells. Additionally, umbilical cord blood stem cells are more prone to damage and death when they are exposed to certain conditions, such as high levels of oxidative stress or certain types of toxins.