The purpose of this study is to test how the skin of night shift workers responds to artificial sunlight (ultraviolet B radiation; UVB) at two different times of the day in comparison to normal day shift workers. After the skin biopsies are obtained, they will be brought to the laboratory to be exposed to UVB radiation and to measure UVB responses.

Inclusion Criteria:

• Male/Female
• Fair skin (Fitzpatrick types I and II)
• Age 18 to 40
• Able to comprehend procedures/risks
• Primarily work and are awake during normal daylight hours (6 am to 6 pm), or primarily work and are awake during night shifts hours (between the hours of 6 pm and 6 am) or may work a mixture of these shifts over the past 3 months. Rotating shifts will be categorized based on the majority of hours worked on average during the last 3 months. Able to fill out a 3-month calendar of work schedule.

Exclusion Criteria:

• Known photosensitivity
• Currently on photosensitizing medications
• Diabetes Mellitus
• On any hormonal agents (e.g., birth control pills)
• History of abnormal scarring
• History of skin infections
• History of skin cancers
• History of sleep disorders such as sleep apnea or insomnia
• Known allergy to lidocaine local anesthetic
• Pregnancy or nursing
• Other serious health issues