Hair grows from cells called hair follicles. Hair follicles are actively and rapidly dividing cells as are tumor/cancer cells. Hence, hair cells are targeted, as are the cancer cells, by chemotherapy drugs. Therefore, during chemotherapy, as a side effect of the drugs, hair cells stop dividing and consequently hair growth stops and hair loss ensues. Hair loss may begin as early few weeks after the chemotherapy treatment. You may notice hair fall out very quickly in clumps or gradually.

The loss of hair may occur all over the body including in armpits, eyelashes etc. The occurrence of hair loss in the body may vary depending on the drugs used. Besides, the extent of the loss is affected by type, dosage, frequency and length of the chemotherapy drug treatment. Hair loss will continue throughout the treatment of the cancer and up to a month afterward. Hair re-grows in about six to eight weeks after the end of the chemotherapy treatment.

On the other hand, radiation therapy against cancer cells, affects only the specific area where the treatment is concentrated. Radiation treatment on the head affects most likely hair on the head only.

As chemotherapy, the extent of hair loss due to radiation treatment is dependent on the radiation type, and dosage. It is possible that cancer patients treated with high radiation dosage may lose hair permanently.