Chemotherapy leads to hair loss because the medicines damage both the cancer cells and the hair-producing cells. Scalp cooling reduces the circulation to the hair roots during the administration of chemotherapy. Because of this, less of the chemicals used for chemotherapy reaches the hair-producing cells, so that they are less damaged. The lower temperature of the scalp also puts the hair-producing cells into ‘hibernation’, so that the damage is further reduced.
When you examine the hair of a patient who had scalp cooling, you can see thinning of the hair shaft in the days after the chemotherapy.
You temporarily see less hair production, but the hair continues to grow. Without scalp cooling, the hair-producing cells become so damaged that the produce very little. Because of this, the hair breaks off before it grows out of the scalp.