Sudden infant death syndrome is the unexplained death of a baby. The baby is usually less than a year old and seems to be healthy. It often happens during sleep. Sudden infant death syndrome also is known as SIDS. It is sometimes called crib death because infants often die in their cribs.

The cause of SIDS is unknown. But it may be caused by problems in the area of an infant's brain that controls breathing and waking up from sleep.

Researchers have found some things that might put babies at higher risk. They've also found some things you can do to help protect your child from SIDS. The most important action may be to place a baby on the back to sleep.

Both physical and sleep factors put an infant at risk of SIDS. These factors vary from child to child.

Physical factors

Physical factors associated with SIDS include:

• Brain defects. Some infants are born with problems that make them more likely to die of SIDS. In many of these babies, the part of the brain that controls breathing and waking up from sleep hasn't developed enough to work properly.
• Low birth weight. Being born early or being part of a multiple birth increases the chances that a baby's brain hasn't fully developed at birth. The baby may have less control over such automatic processes as breathing and heart rate.
• Respiratory infection. Many infants who died of SIDS had recently had a cold. A cold may lead to breathing problems.

Sleep factors

A baby's sleeping position, items in the crib and other conditions may increase the risk of SIDS. Examples include:

• Sleeping on the stomach or side. Babies placed in these positions to sleep might have more trouble breathing than those placed on their backs.
• Sleeping on a soft surface. Lying face down on a fluffy comforter, a soft mattress or a waterbed can block an infant's airway.
• Sharing a bed. The risk of SIDS rises if a baby sleeps in the same bed with parents, siblings or pets. But it may help if the infant sleeps in a separate bed in the same room with parents. That seems to lower the risk of SIDS.
• Overheating. Being too warm while sleeping can increase a baby's risk of SIDS.

SIDS can happen to any infant. But researchers have found several factors that might raise the risk. They include:

• Sex. Boys are slightly more likely than girls to die of SIDS.
• Age. Infants are at higher risk between the second and fourth months of life.
• Race. For reasons that aren't well understood, SIDS occurs more often in Black, Native American and Alaska Native infants.
• Family history. Babies with siblings who died of SIDS are at higher risk of SIDS.
• Secondhand smoke. Babies who live with smokers have a higher risk of SIDS.
• Premature birth. Being born early and having a low birth weight increase a baby's chances of SIDS.

Risk factors in mothers

During pregnancy, mothers also affect their babies' risk of SIDS, especially if they:

• Are younger than 20.
• Smoke cigarettes.
• Use drugs or alcohol.
• Do not receive good medical care while pregnant.

There's no definite way to prevent SIDS. But you can help your baby sleep more safely by following these tips:

• Back to sleep. Place your baby to sleep in the correct position — on the back. Be sure to use the back position every time you or anyone else puts your baby to sleep for the first year of life. Don't trust that others will place your baby to sleep in the correct position: Insist on it. This won't be needed once your baby can roll over both ways without help.

  Don't put your baby on the stomach or side to sleep. Advise a caregiver to only use the stomach position when the baby and caregiver are both in the same room and both are awake. Short periods of "tummy time" help a baby build muscle strength. But the baby should never be left alone during tummy time.

• Keep the crib as bare as possible. Use a firm, flat mattress. Make sure the mattress does not sit at an angle higher than 10 degrees. Avoid placing your baby on thick, fluffy padding, such as lambskin or a thick quilt. Don't leave pillows, fluffy toys or stuffed animals in the crib. They can cause problems with breathing if your baby's face presses against them.
• Don't overheat your baby. To keep your baby warm, try a sleep sack. Or dress your baby in layers instead of using blankets. Don't cover your baby's head.

• Have your baby sleep in your room. If possible, your baby should sleep in your room with you, but not in the same bed. Have your baby sleep alone in a crib or bassinet with a mattress designed for infant bedding. Your baby should sleep in the same room with you for at least six months.

  Adult beds aren't safe for infants. A baby can become trapped and suffocate between the headboard slats. Those are the spaces between the mattress and the bed frame. A baby also can get trapped in the space between the mattress and the wall. And a baby can suffocate if a sleeping parent accidentally rolls over and covers the baby's nose and mouth.

• Breastfeed your baby, if possible. Breastfeeding for at least six months to a year lowers the risk of SIDS.
• Don't use baby monitors and other commercial devices that claim to reduce the risk of SIDS. The American Academy of Pediatrics discourages the use of monitors and other devices. These devices do not prevent SIDS. And they cannot be used instead of safe sleep practices.

• Offer a pacifier. Sucking on a pacifier at nap time or bedtime may reduce the risk of SIDS. Make sure the pacifier does not have a strap or cord. If you're breastfeeding, wait to offer a pacifier until you and your baby have settled into a nursing routine. It usually takes 3 to 4 weeks to set up a nursing routine.

  If your baby is not interested in the pacifier, don't force it. Try again another day. If the pacifier falls out while your baby is sleeping, don't put it back in.

• Vaccinate your baby. There's no evidence that recommended shots to protect against diseases increase the risk of SIDS. Some evidence shows that such shots may help prevent SIDS.

There's no treatment for SIDS. But your baby's pediatrician or other health care professional can talk with you about any risks your baby may have. And there are ways to help your baby sleep safely.

For the first year, always place your baby to sleep on the back. Use a firm, flat mattress and avoid fluffy pads and blankets. Remove all toys and stuffed animals from the crib. Try using a pacifier. Don't cover your baby's head, and make sure your baby doesn't get too hot. Your baby can sleep in your room, but not in your bed. Breastfeeding for at least six months to a year lowers the risk of SIDS. Vaccine shots to protect your baby from diseases also may help prevent SIDS.

After losing a baby to SIDS, getting emotional support is critical. You might be feeling guilty as you grieve the loss of your baby. You're also likely to be dealing with a police investigation into the cause of death as required by law. You might find it comforting to talk to other parents whose lives have been affected by SIDS.

Ask your doctor or other member of your care team to suggest a support group in your area or online. Talking to a trusted friend, mental health professional or clergy member also can help.

Communicate your feelings

If you can, let friends and family know how you're feeling. People want to help, but they might not know how to approach you.

Losing a child can put a terrible strain on a relationship. Be as open as possible with your spouse or partner. Counseling helps some couples understand and express their feelings.

Allow time for healing

Finally, give yourself time to grieve. It's understandable to cry unexpectedly and to find holidays and milestones difficult. You'll also feel tired and drained at times.

You're dealing with a devastating loss. Healing can take time.