Radiation can impact hair, leading to hair loss, though this outcome is not universal. In a medical context, radiation involves targeted energy beams used in treatments like radiation therapy. Whether hair loss occurs, and its extent, depends on specific factors related to the radiation exposure.
How Radiation Affects Hair Growth
Radiation therapy causes hair loss by damaging the rapidly dividing cells within hair follicles. Matrix cells, active during the hair’s anagen (active growth) phase, are highly sensitive to radiation due to their fast division rate. When exposed, these cells can be damaged, disrupting the normal hair growth cycle.
This weakens hair follicles, preventing them from holding existing hair or producing new strands. This disruption can lead to hair shafts breaking or falling out. Hair loss typically begins within one to three weeks after treatment starts. The impact can range from temporary thinning to more complete hair loss if the follicles are severely affected.
Factors Determining Hair Loss
Significant hair loss is primarily associated with medical radiation, such as that used in cancer treatments, rather than typical environmental radiation exposure. Several variables influence whether hair loss occurs, its severity, and its specific location.
The radiation dose is a primary determinant, with higher doses generally leading to more severe and potentially permanent hair loss. Temporary hair thinning can occur with doses as low as 3 to 6 Gray (Gy), while permanent hair loss becomes more probable at doses exceeding 7 Gy. Doses around 43 Gy can result in permanent alopecia for a significant percentage of patients.
The type of radiation used (e.g., X-rays, gamma rays, or proton therapy) also influences the outcome; even proton therapy, designed to spare healthy tissues, can cause hair loss. Hair loss is typically localized to the treated area. For instance, radiation to the head for brain tumors causes scalp hair loss, while treatment to other body parts affects hair only in those specific regions.
The fractionation schedule, or how the total radiation dose is divided over time, also plays a role in hair loss extent. Individual responses to radiation can also vary, indicating differences in sensitivity among patients.
Hair Regrowth After Radiation
For most individuals undergoing therapeutic radiation, hair loss is a temporary side effect. Hair typically begins to regrow within a few months to a year after treatment completion. Noticeable regrowth often appears two to three months after treatment concludes.
The newly regrown hair might exhibit differences in texture, color, or thickness compared to the hair before treatment. It may grow back curlier, thinner, or coarser. These changes are often temporary, and the hair may eventually return to its original characteristics.
Permanent hair loss can occur with very high radiation doses that cause irreversible damage to hair follicles. This outcome is more common with high-dose radiation, particularly when treating areas like the head and neck.