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Why can radiation therapy cause skin reactions and mucositis?

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linear accelerator; external beam radiation therapy — radiation therapy External beam radiation therapy (also known as external beam teletherapy, or long-distance therapy) being delivered using a machine known as a linear accelerator.

Radiation therapy causes skin reactions and mucositis because it targets rapidly dividing cells within the treatment field. While the therapy is designed to damage the DNA of tumor cells to induce cell death, it also affects healthy tissues that have high rates of cellular turnover.12

The skin and the mucous membrane lining the gastrointestinal tract and oral pharynx consist of cells that proliferate quickly. When these areas are exposed to radiation beams, these susceptible cells are easily damaged or killed. This process leads to inflammation of the mucosa, known as mucositis, and various skin reactions. In the gastrointestinal tract, such damage can result in the denudation and ulceration of the lining. These side effects are generally considered acute, or temporary, as they occur in the tissues directly exposed to the radiation.13