Solar ultraviolet radiation (UVR) doses received by individuals are highly influenced by behavioural and environmental factors. This study aimed at quantifying hats' sun protection effectiveness in various exposure conditions, by predicting UVR exposure doses and their anatomical distributions.
A well-defined 3-dimensional head morphology and 4 hat styles (a cap, a helmet, a middle- and a wide-brimmed hat) were added to a previously published model. Midday (12:00-14:00) and daily (08:00-17:00) seasonal UVR doses were estimated at various facial skin zones, with and without hat wear, accounting for each UVR component. Protection effectiveness was calculated by the relative reduction in predicted UVR dose, expressed as a predictive protection factor (PPF).
The unprotected entire face received 2.5 times higher UVR doses during a summer midday compared to a winter midday (3.3 vs 1.3 standard erythema dose [SED]) with highest doses received at the nose (6.1 SED). During a cloudless summer day, the lowest mean UVR dose is received by the entire face protected by a wide-brimmed hat (1.7 SED). No hat reached 100% protection at any facial skin zone (PPF _max : 76%). Hats' sun protection effectiveness varied highly with environmental conditions and was mainly limited by the high contribution of diffuse UVR, irrespective of hat style. Larger brim sizes afforded greater facial protection than smaller brim sizes except around midday when the sun position is high.
Consideration of diffuse and reflected UVR in sun educational messages could improve sun protection effectiveness.