Both chemotherapy and radiation can cause hair loss, but they do it in different ways. Chemotherapy tends to cause hair loss across your entire body, while radiation only causes hair loss in the specific area being treated. The severity, timeline, and likelihood of permanent loss also differ between the two.
Why Chemotherapy Causes Hair Loss
Chemotherapy drugs are designed to kill rapidly dividing cells. That’s how they attack cancer, but hair follicle cells are among the fastest-dividing cells in your body. At any given time, about 90% of the hairs on your scalp are in an active growth phase, during which the cells at the base of each follicle are constantly multiplying to build the hair shaft. Chemo drugs suppress that growth, causing the shaft to weaken, narrow, and eventually break off or fall out at the root.
Hair usually begins falling out two to four weeks after you start chemotherapy. The loss continues throughout treatment and for a few weeks after your last session. It can happen gradually as thinning, or it can come out in clumps over just a few days.
Because chemo circulates through your entire bloodstream, it can affect hair everywhere: your scalp, eyebrows, eyelashes, arms, legs, and pubic area. Not every chemo regimen causes the same degree of loss. Certain drug classes hit hair follicles especially hard. Regimens that include drugs like doxorubicin (a common breast cancer drug) are among the most likely to cause complete hair loss. Taxane-based drugs like docetaxel and paclitaxel also carry high risk, though the pattern varies by specific drug.
Why Radiation Causes Hair Loss
Radiation damages hair follicles through the same basic vulnerability: it disrupts the dividing cells at the base of the follicle, weakening the hair shaft until it breaks or falls out. The key difference is that radiation is a targeted beam, so hair loss only occurs in the area being treated. If you’re receiving radiation to your chest, for instance, your scalp hair won’t be affected. If you’re receiving radiation to your brain, you’ll lose hair on your scalp, but only in the path of the beam.
Hair loss from radiation typically appears within a couple of weeks after treatment ends in the treated area. The pattern often matches the shape of the radiation field quite precisely, which can create a sharply defined patch of hair loss rather than the diffuse thinning or total loss seen with chemo.
Temporary vs. Permanent Loss
With chemotherapy, hair loss is almost always temporary. You can expect regrowth to begin three to six months after treatment ends. Fine, soft “peach fuzz” often appears around six weeks after the final session. However, a small percentage of patients do experience lasting thinning. A study of breast cancer patients found that about 23% of those treated with docetaxel and 10% treated with paclitaxel reported some degree of permanent hair loss on the scalp.
Radiation is where permanent loss becomes a bigger concern, and it depends heavily on the dose. A low single dose (around 2 Gy) typically causes only temporary hair loss. Higher cumulative doses, particularly above 50 to 60 Gy delivered in standard daily fractions, can destroy the follicle’s ability to regenerate entirely. Many radiation treatment plans for brain tumors fall in a range where partial permanent thinning in the treated area is possible. Your radiation oncologist can often predict which areas are most at risk based on the dose map.
Scalp Cooling for Chemotherapy
Scalp cooling caps are the main preventive option for chemotherapy-related hair loss. These tightly fitting caps circulate cold fluid around your head during infusion, narrowing blood vessels in the scalp so less of the drug reaches your hair follicles. They don’t work perfectly for every regimen, but the overall success rate is promising.
In a retrospective study of patients using cold caps, about 92% retained enough hair to consider the outcome successful. Results were best with taxane-based regimens: roughly 96% of patients on docetaxel or paclitaxel kept most of their hair. For those on doxorubicin-containing regimens, the success rate dropped to about 71%, which still represents meaningful hair preservation for many people. Cold caps require commitment. They need to be worn before, during, and after each infusion session, and the cold can be uncomfortable. There is currently no widely used equivalent for preventing radiation-related hair loss.
What Regrowth Looks Like
After chemotherapy, new hair frequently comes in looking different from what you had before. Straight hair may grow back curly, a phenomenon commonly called “chemo curls.” The color can shift too: brunettes sometimes notice reddish or lighter tones. Hair often feels finer, more fragile, or grows in uneven patches initially. These changes happen because residual effects of the drugs temporarily alter how follicle cells produce the hair shaft. For most people, texture and color gradually return to something closer to their pre-treatment hair over the following year or so.
With radiation, regrowth in the treated area depends on the dose that area received. Lower-dose zones may see full recovery within several months, while higher-dose zones may produce thinner, sparser hair or none at all. The regrowth pattern can be patchy, reflecting the uneven dose distribution across the treatment field.
Eyebrows, Eyelashes, and Body Hair
Chemotherapy can cause loss of eyebrows and eyelashes along with scalp hair, and this is one of the side effects patients find most distressing. These hairs typically regrow after treatment, though they may take longer than scalp hair and come back thinner at first. Options during the waiting period include cosmetic tattooing, specialized makeup, and prescription growth serums, though research on effectiveness specifically in cancer patients is still limited.
Radiation generally doesn’t affect eyebrows or eyelashes unless the treatment field directly targets the face or orbital area. The same principle applies to all body hair: radiation only damages follicles within its path, so body hair loss is limited to the treatment site.