Study of Skin Cells That Stop Replicating (Senescent) During Wound Healing

Background: Cellular senescence is the aging of cells. It is a complex process that may be connected with aging and age-related diseases. It is unknown if these cells appear around wound sites in humans a few days after skin injury and if there are differences in young and old individuals. This study is being done to look at how cells in your body respond to small skin wounds. This information may help treat age-related diseases. Objective: To study how cells in the body respond to small skin wounds. Eligibility: Healthy adults ages 20-39 or 70+ Design: Participants will be screened with medical history, physical exam, and blood sample. They will fast before the screening visit. Women will have a urine pregnancy test. Participants will have 3 study visits over about 3 weeks. Visits 1 and 2: Participants will fast before and have blood taken. Women will have a urine test. All participants will have 2 skin biopsies. A spot on the upper arm will be numbed. Two small pieces of skin will be removed. They will keep the area covered until the next visit. Visit 3: Participants will have their vital signs taken. Their biopsy wounds will be measured and photographed.