When ordinary people hear the word “cancer patient” in film, television or reality, nine times out of ten, the image that comes to mind is the appearance of hair falling out. This is also the most visual change in the appearance of cancer patients after treatment. Then why do cancer patients lose their hair after chemotherapy? Do all chemotherapy treatments cause hair loss? Will the hair that has fallen out grow back? Will the hair that grows back be the same? One of the characteristics of cancer cells is that they grow rapidly, keep dividing and grow rapidly. So when anti-cancer drugs were designed, these traditional anti-cancer drugs were designed to specifically attack fast-growing cells in the expectation that they would only kill the cancer cells and not cause harm to the majority of cells that normally grow slowly. However, our body, by chance, has some cells that normally grow rapidly and renew quickly. For example, bone marrow cells, hair follicle cells, oral mucosa cells, gastrointestinal epithelial cells, female reproductive tract cells, and so on. After conventional chemotherapy drugs are injected into the body from a vein, they quickly spread throughout the body, and while killing cancer cells, they attack these fast-growing cells without difference, so common side effects appear, such as bone marrow suppression and dry mouth. This includes hair loss. Understanding the characteristics of hair loss from chemotherapy helps cancer patients or family members prepare emotionally and psychologically. This is because many people can tolerate other side effects of chemotherapy, but have difficulty tolerating hair loss, which affects their appearance the most, especially women. There are even patients who refuse to continue treatment because of hair loss. Our human scalp has about 100,000 hairs, and a normal person loses 100 to 150 hairs a day. New hair will grow to make up for the hair that falls out. There are two ways that a patient can lose hair after receiving chemotherapy. One is that the hair tapers at the maximum dose of chemotherapy and then breaks down the middle. The other is that the hair roots are severely inhibited and fall out directly from the roots. Hair loss is also not just hair, but eyebrows, eyelashes, and pubic hair can all fall out to varying degrees. In some people, all the hair falls out quickly within 1 to 3 weeks after chemotherapy, while in others it falls out slowly and continues for a long time. This hair loss is usually most noticeable when combing or washing the hair, so cancer patients who wash their hair less frequently may see a lot of hair fall out during a single wash. Some medications have unique properties, so the hair loss they bring about can also be very specific. For example, cyclophosphamide, a commonly used chemotherapy drug, causes hair thinning but not complete hair loss. Fluorouracil, on the other hand, does not cause hair loss. Adriamycin will cause hair to taper in the first 3 weeks and then fall out completely overnight. Paclitaxel can cause hair loss overnight, and many patients treated with paclitaxel will find that they wake up early in the morning with all their hair falling out. There are also chemotherapy drugs that do not cause hair loss, but can cause hair to become lighter or thicker in color. For example, the commonly used drugs cisplatin and cyclophosphamide can cause gray or white hair. Methotrexate can cause thickening of hair color and lighter hair, as is more apparent in blond Westerners, appearing as one darker and one lighter strand, known as star-spangled syndrome. Although hair loss after chemotherapy can seem scary and disturbing, hair that has fallen out will grow back when chemotherapy is stopped or even later in the course of chemotherapy (don’t worry, this is not a sign that the chemotherapy is not working), so there is nothing to worry about. After chemotherapy is over, usually within a few weeks, most people’s hair will grow back one by one. However, you may notice that the hair quality becomes different. Some people’s hair becomes thinner, others thicker, and others find that their hair becomes curlier. After six months to a year, the majority of hair will return to the same as before. Therefore, patients or family members who are unfortunate enough to have cancer should not worry too much about hair loss.