A woman is born with just so many egg cells, called oocytes. When she begins ovulating, she has about 400. Even though that may seem like a lot, considering the few that would ever be fertilized, scientists have found that loss of oocytes influences a woman’s health. Early loss of oocytes leads to early menopause and infertility. A study by researcher Jonathan Tilly, Harvard Medical School associate professor of obstetrics, gynecology and reproductive biology at Massachusetts General Hospital, has found that chemicals in cigarette smoke and environmental pollutants can trigger egg loss. “There’s a longstanding relationship between smoking and early menopause,” Tilly said. Now, with a study that appeared in the August 2001 issue of Nature Genetics, Tilly has identified a genetic pathway that helps explain that relationship.