Crib death (SIDS, crib death) is not a medical matter. It is caused by poisonous gases generated in the baby's sleeping environment. The gases concerned are phosphines, arsines and stibines, which are all extremely toxic nerve gases. The gases are produced in a baby's crib (or other sleeping environment) by the action of common household fungus on compounds of phosphorus, arsenic and antimony present in the mattress and in certain other bedding. The danger of crib death increases as a mattress is re-used from one baby to the next. Babies can be protected from this gaseous poisoning by enclosing mattresses in a gas-impermeable cover which is itself not capable of the gas generation concerned, and using on top of the wrapped mattress specified bedding which is also not capable of that gas generation. For details of the mattress-wrapping protocol, click on  How to prevent crib death (SIDS). Breastfeeding does not prevent crib death. Smoking does not cause crib death. Sleeping a baby with feet to the foot of the crib does not prevent crib death. Face-up sleeping is only a partial preventive against crib death.  Many babies have died sleeping face-up on unwrapped mattresses. Crib death is not a syndrome. The term SIDS (Sudden Infant Death Syndrome) is a misnomer. The physiological effect of the toxic gases which cause crib death is to de-activate a certain vital enzyme in the body.  As the gas is ingested into the baby's body (by breathing in and/or absorption through the skin), more and more of the enzyme is de-activated, until eventually there is insufficient enzyme left to support life. The function of the enzyme is to ensure that nerve impulses from the brain are transmitted to the various parts of the body which act upon the impulses.  If sufficient gas is ingested, the nerve impulses "telling" the lungs to breathe don't reach the lungs and the baby stops breathing. Shortly after this occurs, heart function ceases, and death follows very soon afterwards. This explains why crib death babies do not show physical symptoms.  The babies were not ill in the medical or physiological sense; they were poisoned by environmental gaseous poisoning.