There’s no doubt that overheating from too many night colors, too many blankets, and too high a room temperature is a contributory factor, as SIDS is much more common in overheated babies. (The risk of overheating alone, however, is less than that from sleeping position and smoking.) Two- third of crib deaths occur in winter, when babies may wrapped up too warmly.
Many parents increase the amount of bedding when a baby is unwell, but this is not what your baby needs. High temperature plus infection in babies over ten weeks old greatly increases the risk of the crib death. If heat loss is prevented, the body temperature of a restless baby with an infection will rise by at least 1°C per hour. A baby loses most heat from its face, chest, and abdomen, so lying on the back allows body temperature to be better controlled.
Baby nests, sheepskins, quilts, and comforters are all heat insulators, and should not be used for young babies, because they prevent heat loss. You need not keep your baby’s room warmer than the rest of your house; just make sure your baby has enough covering (see below). If you do have a separate heater in the nursery, use a thermostatically controlled one that will switch off if the room gets too warm and switch back on again as it cools down.