Treatment of chronic pain is a major clinical challenge since chronic pain is frequent and leads to deterioration of quality of life. An injury or wound can lead to long term changes in the nervous system that make the skin more sensitive at and near the injury; this is termed hyperalgesia and occurs through long term depotentiation (LTP), i.e., a change in the synaptic interaction between neurons.

Opioids are the gold standard for the symptomatic therapy of moderate to severe pain. Now, in animal studies the investigators have discovered previously unrecognized effects of opioids.

UV-B irradaition of the skin of the thigh is an established model of priamary and secondary hyperalgeisa in humans. The investigators want to test the influence of remifentanil, an ultra-short acting opioid, on hyperalgesia observed after UV-B irradiation in human volunteers in a double blind cross-over prospective active placebo controlled clinical trial.

Inclusion Criteria:

• Body mass index between 15th and 85th percentile
• Normal findings in the medical history and physical examination
• Drug free for 1 week prior to the study day

Exclusion Criteria:

• Regular use of medication especially analgesics
• Abuse of alcoholic beverages, drug abuse
• History of asthma
• Participation in a clinical trial in the 2 weeks preceding the study
• Symptoms of a clinically relevant illness in the 2 weeks before the first study day
• Resting systolic blood pressure > 135 mmHg or diastolic blood pressure > 85 mmHg
• Acute skin diseases like sunburn on the relevant areas or skin lesions
• Pregnancy or breast feeding
• UV sensitive skin conditions, like Xeroderma pigmentosa