Permeability barrier function of skin exposed to ionizing radiation.

OBJECTIVE To characterize the epidermal permeability barrier function of skin during exposure to ionizing radiation. DESIGN A prospective cohort study. SETTING University hospital medical center. PATIENTS Fifteen women receiving local radiation therapy (5000-6000 rad [50-60 Gy]) following breast-conserving surgery for breast cancer. MAIN OUTCOME MEASURES Clinical symptoms and transepidermal water loss (TEWL). RESULTS Epidermal permeability barrier function is impaired in patients who exhibit clinical signs of radiation dermatitis. The functional damage to the stratum corneum induced by ionizing radiation occurs with a delayed course, starting within a mean period of 11 days and reaching maximal values after a mean period of 27 days (range, 13-75 days). The onset of TEWL increase precedes the onset of radiation dermatitis and the maximal TEWL measurements precede the peak of skin changes. Patients with an early onset of TEWL increase show a longer duration of skin symptoms. CONCLUSIONS Skin changes caused by radiation dermatitis are associated with an increase in TEWL. The barrier impairment is comparable to the changes observed with UV radiation exposure but exhibits an even more delayed course. Our results suggest that preservation of the epidermal permeability barrier function by topical treatment may ameliorate radiation dermatitis.