Objective:To assess the effect of use (washing and wearing) on the photoprotection provided by a cotton fabric.Methods:Twenty jersey‐knit pure cotton T‐shirts were worn for 4–8 hours per week and washed weekly for 10 weeks. Fabric samples taken before and after use were compared.Main outcome measures: Fabric ultraviolet protection factor (UPF) was calculated from spectrophotometric ultraviolet radiation transmission data. Changes in fabric structure and hole size were determined for samples from one T‐shirt by light microscopy and image analysis.Results:UPF increased consistently and significantly after use, from a mean of 19.0 to 40.6. A corresponding reduction in fabric hole area was seen under the light microscope and confirmed on image analysis (from 8.0% to 3.9% of total image area).Conclusion:UPF of pure cotton garments may improve after use, at least in the short term. The increase is mostly accounted for by reduction in fabric hole area due to shrinkage.