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 non-laminated glass.
Objectives: To determine which types of glass provide most protection from UVA with particular reference to implications for patients with polymorphic light eruption (PLE).
Methods: The percentage transmission of UVA was determined for a selection of glass, both laminated and non-laminated and with differing colour tints.
Results: Laminated glass transmits less UVA than non-laminated glass. Tinted glass transmits less UVA than clear glass. Non-laminated clear glass transmitted the highest percentage of UVA (62.8%) and grey laminated glass the lowest (0.9%). A dose of 5 Jcm-2 UVA, enough to trigger PLE in some patients, could be transmitted through clear non-laminated glass in 30 minutes but would take 50 hours 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.
Hampton PJ, Farr PM, Diffey BL, Lloyd JJ. Implication of UVA exposure in vehicles for photosensitive patients. British Journal of Dermatology 2004; 151: 873-876.
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