The glow of city lights blotting out stars in the night sky has frustrated many a stargazer, but recent studies have shown that “light pollution”--defined as excess or obtrusive light at night--can actually have serious health effects. Researchers have found that exposure to bright nocturnal light can decrease the human body’s production of melatonin, a hormone secreted at night that regulates our sleep-wake cycles. And decreased melatonin production has in turn been linked to higher rates of breast cancer in women.

“Light at night is now clearly a risk factor for breast cancer,”

breast cancer rates were significantly higher in industrialized countries,

female night shift workers have a 50 percent greater risk of developing breast cancer

Even bright light from a trip to the bathroom can have an affect, so dim nightlights are recommended for night lighting.

Light pollution causes other problems besides increased cancer risks.