The investigators want to study if nanoparticles of titaniumdioxide are penetrating skin when the skin is intact and when the skin is sunburned. The hypothesis is "Does nanotitandioxide penetrate intact or sunburned skin?"

In this pilotstudy there are two human volunteers. The study comprises two phases. The first phase: The volunteers are applying a commercially available sunscreen lotion containing titanium dioxide nano particles 6 times a day for one week in an area of the back that is 30x20 cm. Before the first application a 2mm punch biopsy is to be taken and examined by scanning electron microscopy. After applying sunscreen lotion for a week, a new biopsy will be taken in order to see how far down in the skin the particles have penetrated. In the second phase: An artificial sunburn will be induced in the same area of the back. They will thereafter apply the sunscreen lotion 6 times a day like in the first phase. After two days (estimated time of maximum skin irritation) a biopsy will be taken in order to see if the nanoparticles have penetrated down in the layers of the skin, and the investigators will also take a biopsy after a full week of applying the sunscreen lotion. The investigators will also examine the urine, before and after the use of sunscreen, to see if the investigators can find the particles there.

Inclusion Criteria:

• Healthy men above 50 years old

2 healthy males older than 50 years