Inclusion Criteria:  Healthy women between the ages of 18 and 45 years (Controls), taking oral contraceptive or with regular menses every 26-34 days Women between the ages of 18 and 45 years with endometriosis (diagnosis by prior laparoscopy by subject's own physician <5 years prior, and reported by the subject to the researchers) Tylenol if the subject has acute pain is allowed Contraceptive use is allowed  Exclusion Criteria:  Use of nicotine-containing products (e.g. smoking, chewing tobacco, etc.) Diabetes (HbA1C 6.5%) BP>140/90 Taking pharmacotherapy that could alter peripheral vascular control (e.g. insulin sensitizing, cardiovascular medications) Pregnancy Breastfeeding Taking illicit and/or recreational drugs Abnormal liver function Rash, skin disease, disorders of pigmentation, known skin allergies Diagnosed or suspected metabolic or cardiovascular disease Persistent unexplained elevations of serum transaminases Known allergy to latex or investigative substances (including salsalate or simvastatin) History of gastrointestinal bleeding