At last, there's a true breakthrough in the battle to understand Sudden Infant Death Syndrome (SIDS). Researchers at Children's Hospital Boston were able to link abnormalities in the brain's serotonin system  -- which regulates breathing, blood pressure, body heat, sensitivity to carbon dioxide, and arousal  -- to the deadly syndrome. "Serotonin is like an alarm," says study author Hannah Kinney, M.D. If babies sleep face down or get their faces covered with bedding, they are in danger of rebreathing their own exhaled carbon dioxide, cutting off their oxygen intake. Normally, when carbon dioxide levels rise, serotonin stimulates the baby to wake up, turn his head, and start breathing faster. For SIDS babies, that alarm doesn't go off. "We can now say SIDS is not a freak thing. It's a disease," adds Dr. Kinney. "That makes it more important than ever to follow the SIDS precautions."

• Put your baby to sleep on his back.
• Never smoke around your baby.
• Consider giving a pacifier at bedtime  -- pacifier use during sleep may protect infants from SIDS.
• Don't overheat your baby's room; keep it between 68° and 72°.
• Don't use soft bedding, pillows, blankets, or toys in the crib.