BACKGROUND Clothing fabrics have long been considered effective protection against short-term and long-term sun damage. Recently, special "highly UV-protective" fabrics have been developed specifically for photosensitive patients. OBJECTIVE To determine if one such fabric will protect hairless mice against (pre)malignant lesions under conditions that will produce skin cancers through a typical summer fabric of moderate sun protection factor (SPF). METHODS After prior determination of minimal erythemal dose, four sets of 10 animals were divided into the following groups: (A) dark control (no irradiation); (B) positive control (no fabric); (C) "typical summer" fabric (SPF = 6.5 +/- 1.0); and (D) "special" fabric (SPF > 30 across a broad spectrum). Mice were irradiated on the dorsal surface 5 days per week, with biweekly incremental increases (roughly 20% of the starting dose), for 12 weeks. Group B started at 6.3 J/cm2, with biweekly increases of 1.45 J/cm2 (total dose, 596 J/cm2); groups After irradiation, mice were observed for clinical and histologic signs of pre(malignant lesions for an additional 12 weeks. RESULTS At the end of the 12-week irradiation period, nine mice in group B and six mice in group C had actinic keratosis-like lesions, whereas one mouse in group B and two mice in group C had squamous cell carcinoma. By week 24, all mice in groups B and C had squamous cell carcinoma. Mice in groups A and D showed no discernable reaction at any time. Biopsy specimens confirmed the clinical results. CONCLUSIONS Typical summer clothing fabrics may offer inadequate protection against skin cancer and pose high risk to chronically photosensitive patients. The use of appropriate sun protective apparel should offer effective protection to photosensitive patients against short-term and long-term photodamage.