Chemotherapy is widely known for causing hair loss (alopecia) because the drugs target rapidly dividing cells throughout the body. While hair loss is the most visible side effect, the quality of the hair that regrows is also frequently altered. Chemotherapy can definitively change both the hair’s color and texture. These changes occur because the treatment affects the cells responsible for hair growth and pigmentation, leading to a temporary shift in the hair’s characteristics.
The Science Behind Pigment Changes
Hair color is determined by melanin, a pigment produced by specialized cells called melanocytes within the hair follicle. Chemotherapy drugs attack rapidly dividing cells, making both the hair shaft matrix cells and the melanocytes highly susceptible to damage.
When chemotherapy is administered, the drugs temporarily impair these pigment-producing melanocytes. This disruption halts or significantly reduces the cell’s ability to create and transfer melanin into the forming hair shaft. Melanocyte function is often compromised first due to their sensitivity to cellular stress.
This temporary damage resets the hair follicle’s pigment production cycle. When hair regrows, the new hair shaft may lack the normal amount of melanin, resulting in the visible color changes observed.
Common Alterations in Hair Color and Texture
The most common color change observed is acquired graying, where the hair returns white or a shade of gray. This occurs because chemotherapy severely damages or shuts down the melanocytes, preventing pigment incorporation into the new hair strand. The hair shaft is colorless without melanin, appearing white or gray when mixed with existing pigmented hairs.
In some cases, hair regrows a darker shade than the original color, known as hyperpigmentation. This darkening may be related to an overcompensation effect as recovering melanocytes temporarily produce an increased concentration of pigment. Targeted therapies have also been associated with unexpected hair darkening or the repigmentation of previously gray hair.
A significant alteration is the change in hair texture, often nicknamed “chemo curl.” Hair that was once straight may return curly, or naturally curly hair may regrow straighter. This shift is caused by temporary structural damage to the hair follicle, which alters the differentiation pattern of the stem cells. The damage changes the hair shaft’s cross-section from a rounder shape to a more oval one, resulting in a curl. The new hair, sometimes called “virgin hair,” can look and feel completely different from the hair the patient had before treatment.
Duration and Reversal of Color Alterations
For most patients, the changes in hair color and texture are temporary, as the hair follicles and melanocytes heal over time. New hair typically begins to appear within three to six months after treatment completion, starting as a fine layer of “peach fuzz” that gradually thickens and strengthens.
The return of the original color is a gradual process coinciding with the full recovery of the melanocytes and the stabilization of the hair growth cycle. It can take several months, often up to a year, for the hair to revert entirely to its pre-treatment color and texture. As the altered hair grows out, hair returning from the root begins to incorporate the normal amount of melanin.
While rare, permanent changes in color or texture are possible, particularly following high-dose chemotherapy regimens. The likelihood of a permanent change depends on the specific drugs used, the total dose administered, and individual patient factors. However, the vast majority of patients can expect their hair to eventually resemble their original characteristics.