Hair Loss and Chemotherapy What is hair loss and how is chemotherapy related? Believe it or not, hair loss (alopecia) due to chemotherapy is one of the most distressing side effects of chemo treatments. Hair loss happens because the chemotherapy affects all cells in the body, not just the cancer cells. The lining of the mouth, stomach, and the hair follicles are especially sensitive because those cells multiply rapidly just like the cancer cells. The difference is that the normal cells will repair themselves, making these side effects temporary. Hair loss does not occur with all chemotherapy. Whether or not your hair remains as it is, thins or falls out, depends on the drugs and dosages. Hair loss may occur as early as the second or third week after the first cycle of chemotherapy, although it may not happen until after the second cycle of chemotherapy. Hair loss can be sudden or slow. You may loose all of your hair or just some of it. Often it comes out in clumps rather than an even pattern. Information provided by: Chemocare.com