Why does chemotherapy cause hair loss?
Nov 05, 2025
Source: Cainiu Health
Dr. Yang Ziqi
Introduction
The reasons for hair loss caused by chemotherapy generally include the drug's attack on rapidly dividing cells, disruption of the hair follicle cell cycle, direct toxicity of the medication to hair follicles, individual differences in drug sensitivity, and the impact of drug dosage and treatment duration. Chemotherapy drugs primarily target rapidly dividing cancer cells in the body, but hair follicle cells also divide rapidly, making it difficult for the drugs to precisely distinguish between them.
Chemotherapy-induced hair loss is generally caused by several factors, including the drug's attack on rapidly dividing cells, disruption of the hair follicle cell cycle, direct toxicity of the medication to hair follicles, individual differences in drug sensitivity, and the impact of drug dosage and treatment duration. A detailed analysis is as follows:
1. Attack on rapidly dividing cells: Chemotherapy drugs primarily target rapidly dividing cancer cells. However, hair follicle cells also divide rapidly. The drugs cannot precisely distinguish between cancer cells and hair follicle cells, leading to unintended damage to the hair follicles. This impairs follicular function and results in hair loss.
2. Disruption of the hair follicle cell cycle: Normal hair growth involves three phases—growth (anagen), regression (catagen), and resting (telogen). Chemotherapy drugs disrupt this natural cycle, forcing a large number of hairs in the growth phase to prematurely enter the resting phase. Deprived of nutrients, these hairs shed quickly, resulting in noticeable hair thinning within a short period.
3. Direct toxicity of drugs to hair follicles: Some chemotherapy agents are inherently toxic and can directly damage the epithelial cells of hair follicles, compromising the structural integrity of the follicles. This interferes with normal hair growth and, in severe cases, may temporarily impair the follicles' regenerative capacity, leading to hair loss.
4. Individual differences in drug sensitivity: People vary in their response to chemotherapy drugs. In some individuals, hair follicle cells are more sensitive to the drugs, resulting in more severe hair loss under the same drug regimen and dosage. Others with lower sensitivity may experience only mild hair thinning or even no significant hair loss at all.
5. Impact of drug dosage and treatment duration: Higher drug doses and longer treatment courses lead to greater cumulative damage to hair follicle cells, increasing both the likelihood and severity of hair loss. With short-term, low-dose chemotherapy, follicular damage is milder, hair loss may be minimal or absent, and hair recovery after stopping the drug tends to be faster.
During chemotherapy, it is advisable to use gentle shampoo products and avoid frequent perming or dyeing of hair. After treatment ends, most people will gradually regrow their hair. Maintaining good scalp hygiene and consuming a balanced diet rich in nutrients can support follicular repair and promote hair regrowth.
