Implication for photosensitive patients of ultraviolet A exposure in vehicles

Summary Background Photosensitive patients sometimes report disease flares during journeys by car. Window glass blocks all UVB but not all UVA. All car windscreens are made from laminated glass. Side and rear windows are usually made of nonlaminated glass. Objectives To determine which types of glass provide most protection from UVA with particular reference to the implications for patients with polymorphic light eruption (PLE). Methods The percentage transmission of UVA was determined for a selection of glass, both laminated and nonlaminated, and with differing colour tints. Results Laminated glass transmits less UVA than nonlaminated glass. Tinted glass transmits less UVA than clear glass. Nonlaminated clear glass transmitted the highest percentage of UVA (62·8%) and grey laminated glass the lowest (0·9%). A dose of 5 J cm−2 UVA, enough to trigger PLE in some patients, could be transmitted through clear nonlaminated glass in 30 min but would take 50 h through grey laminated glass. Conclusion Patients with severe UVA‐induced PLE and other photosensitivity disorders may have disease flares from solar UVA transmission through side‐window glass. Protective measures such as wearing long‐sleeved clothing, keeping the arm beneath the bottom of the window aperture, or choosing tinted and laminated car windows may be helpful.