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.

* INCLUSION CRITERIA: * Age 20 - 39 years or age 70 years and older. * Healthy (see exclusion criteria below). * Are able to understand the study risks and procedures, and consent to participate in the study. * Are able to read and speak English. * Caucasian or African American * Previous enrolled participants. EXCLUSION CRITERIA (SCREENING VISIT): * A medical condition that requires the use of chronic anticoagulant medication use such as warfarin, clopidogrel, heparin or antiplatelet agents other than low dose aspirin (81mg). * History of increased bleeding due to either a known medical condition or an undiagnosed cause. * A medical condition that causes impaired wound healing such as diabetes. * Current androgenic/anabolic and/or corticosteroid use or use within 90 days of the procedure (ocular corticosteroid use okay). * Current antibiotic or anti-viral use or use within 60 days of the procedure. * Active infections or chronic skin conditions that would prevent access to the biopsy area. * Taking non-steroidal anti-inflammatory agents (NSAIDs) such as Motrin (Ibuprofen), Advil (Ibuprofen) or Naprosyn (Naproxen) and the participant is unable to stop taking them 3 days before the biopsy and 1 day after the biopsy procedure. * Taking more than 81 mg of aspirin a day and the participant is unable to stop taking it for 3 days before the biopsy and 1 day after the biopsy procedure. * Allergic to Lidocaine (Xylocaine) or any other local anesthetic or the participant has had in the past a severe allergic reaction to similar drugs. * Allergic to topical betadine solution. * Severe allergy to adhesives found in tape. * HIV virus infection. * Hepatitis B or C or exposure within 6 months of visit. * History of diabetes (requiring any medical treatment other than diet and exercise) or fasting plasma glucose is \>=126 mg/dL or HbA1c \>= 6.5%. * Clinically significant hormonal dysfunction (self-reported or laboratory values out of range. Mild hypothyroidism (TSH \< 10 microIU/mL) in participants over 60 is not considered exclusion). * Kidney disease (Creatinine \>1.5 mg/dl or calculated creatinine clearance \< 50 cc/min) * Liver disease (Bilirubin \> 1.5 mg/dl (unless higher levels can be ascribed to Gilbert s disease); ALT, AST or alkaline phosphatase twice the normal serum concentration). * Severe gastrointestinal diseases such as Crohn s disease or ulcerative colitis requiring continuous treatment. * History of severe pulmonary disease such as chronic obstructive pulmonary disease (COPD) or asthma requiring continuous medication use. * History of severe psychiatric conditions associated with behavioral problems or requiring chronic medical treatment. * Currently pregnant or breastfeeding. * Participants with history of skin keloid formation during wound healing * Current illness that as judged by the study physician substantially increases the risks associated the skin biopsy(s) (active infections, allergies, etc.).