Radiation therapy is a highly targeted medical treatment that uses high-energy waves, like X-rays or protons, to destroy cancer cells or shrink tumors. The treatment is effective because it damages the DNA of fast-growing cells, preventing them from dividing and multiplying. When considering this treatment, a common question is whether it causes hair loss; the answer is yes, but this side effect is highly conditional and depends entirely on the location being treated.
The Specificity of Radiation-Induced Hair Loss
Hair loss resulting from radiation therapy, known as alopecia, is almost exclusively confined to the precise area receiving the radiation beam. Unlike chemotherapy, which is a systemic treatment that can cause hair loss all over the body, radiation only affects the path of the beam through the body. This localized effect occurs because the radiation damages the rapidly dividing cells within the hair follicles responsible for hair growth.
The hair follicles in the anagen, or growth, phase are particularly sensitive to this damage, which leads to the hair shaft weakening and eventually shedding. Hair loss typically begins two to three weeks after the start of treatment, as the damaged hair completes its growth cycle. In some cases, hair loss can also occur at the radiation exit site. The extent of the hair loss is directly related to the size of the treatment field and the total radiation dose delivered to the area.
Factors Determining Regrowth
The most significant factor determining whether hair loss is temporary or permanent is the total cumulative radiation dose delivered to the hair follicle. Lower doses generally cause temporary hair thinning or loss, as the follicular cells are stunned but not permanently destroyed. Once treatment is complete, these cells can recover, and the hair follicle can resume its normal function.
Higher doses carry an increased risk of permanent alopecia because they can irreversibly damage the follicular stem cells. While the exact threshold varies among individuals and treatment types, doses above 40 Gray (Gy) often result in a high risk of permanent hair loss in the treated area. Studies suggest that a dose of approximately 43 Gy delivered to the hair follicles is associated with a 50% chance of permanent hair loss.
For temporary hair loss, regrowth typically begins within three to six months after the completion of the radiation therapy course. When the hair grows back, it may present with different characteristics than before treatment. Patients may notice changes in the hair’s texture, such as it becoming curlier, or differences in its color or overall thickness.
Strategies for Scalp Care and Comfort
During the treatment period, treating the scalp with extreme gentleness is a practical strategy for comfort and to minimize further irritation.
Hair Washing and Styling
It is recommended to use only a mild, pH-neutral shampoo and to wash the hair less frequently and with minimal friction. Instead of using a harsh towel, gently pat the scalp dry. Avoid using heated styling tools such as blow dryers, curling irons, or straighteners.
Protection and Chemical Avoidance
Patients should avoid chemical treatments like hair coloring, perms, or bleaching throughout the radiation course, as these can be too harsh for the sensitive skin. Protecting the scalp from environmental factors is also important. This includes wearing a hat, scarf, or turban to shield the skin from direct sun exposure and cold temperatures. Some individuals find it helpful to cut their hair short before treatment begins, which can make the shedding process feel less jarring.
Comfort Measures
If the scalp becomes tender or itchy, applying gentle, unperfumed lotions or conditioners can help soothe the irritation. For those considering a wig, selecting and fitting it before hair loss occurs allows for a better match to the original hair color and style. Ultimately, open communication with the healthcare team about any scalp discomfort or concerns regarding hair loss is the best approach to managing this side effect.