I wonder if donating bone marrow to my cousin will be dangerous, such as inflammation. I heard that I have to make a hole in the bone.

No, it just hurts. Donating bone marrow will not affect people's health. Many people think that donating bone marrow is extracting spinal cord, which is a complete misunderstanding. Bone marrow transplantation needs red bone marrow, which is hematopoietic stem cells. An adult's bone marrow weighs 3 kg, and donors who provide less than 10 g of bone marrow hematopoietic stem cells can save the life of a leukemia patient. So it will not weaken its immune function and hematopoietic capacity. Bone marrow is a kind of tissue with strong regenerative ability. The average healthy person can make up the donated stem cells in about ten days after donating hematopoietic stem cells. Please adopt it, hehe.