Sunscreen use at Danish beaches and how to improve coverage.

Exposure to ultraviolet radiation (UVR) from the sun is the main risk factor for development of skin cancer. The incidence of skin cancer in Denmark and worldwide is high and increasing. The overall aim was to achieve basic knowledge about sun protection with sunscreen among beachgoers in Denmark. Other aims were to establish a method to investigate sunscreen distribution on the body and to test two approaches to optimize the used amount and body distribution of sunscreen. Furthermore, time and duration of a beach visit and use of protective clothes among beachgoers were determined to investigate the risk the beachgoers expose themselves to. 
Of the counted number of beachgoers 46% were at the beach between noon and 3 p.m. where the UVR is strongest and a mean beach visit lasted 142 minutes. In the middle of the day 90% of the beachgoers wore swimwear and sunscreen application was their only possible sun protection. More beachgoers wore protective clothes in the morning and late afternoon.
 Seventy-eight percent of women wearing swimwear reported sunscreen use at the beach and 49% of men reported sunscreen use. They used a sunscreen with a median sun protection factor (SPF) of 20 (interquartile range: 15-30). The effective SPF probably decreases exponentially with decreasing quantity of sunscreen applied. Users at the beach applied a mean quantity of 0.57 mg/cm (standard deviation 0.31 mg/cm) to their sun accessible skin, i.e. skin not covered by swimwear or scalp hair, providing a mean effective SPF of 2.3. Both SPF chosen and quantity applied were independent of sex. 
Two approaches to increase sunscreen use was tested; the rule of thumb: "Fill up a handful of sunscreen and spread it all over your body", and a recommendation to apply sunscreen two consecutive times. Both strategies increased the total amount of sunscreen significantly. The instruction: "Fill up a handful of sunscreen and spread it all over your body" increased the median quantity of sunscreen to 0.87 mg/cm whereas double application increased the quantity to 1.10 mg/cm. Sunscreen with a label SPF of 20 applied in a quantity of 0.87 mg/cm provided an effective SPF of 3.7. Applied in a quantity of 1.10 mg/cm provided an effective SPF of 5.2. 
A method based on a link between darkness of skin in black light illumination and the quantity of sunscreen applied was established and made it possible to investigate the distribution of sunscreen on the body. Sunscreen was very unevenly applied both after application of a handful and after double application. The face and the front of the trunk were generally well covered whereas the back of the trunk was poorly covered. After a single application, either as at the beach or with the use of a handful of sunscreen, about one fifth of the total accessible skin was left without sunscreen. After double application only about a 9% of the accessible skin was left uncovered. As especially missed areas are at risk of getting sunburned double application seems to be the better of the two tested strategies to improve coverage.