There are two main myths about Sudden Unexpected Death of an Infant (SUDI, also known as SIDS (Sudden infant death) and as cot death) that cause some parents to avoid the safety advice.
One myth is that there is more risk from choking if a baby sleeps on their back. This is not true. Babies gag and swallow in all sleeping positions.
That is how they protect their airways. Also, the windpipe is above the food tube when babies lie on their back. In this position, the gagging reflexes are stronger and it is easier for babies to keep their airways safe.
To sleep your baby on the side is false protection. It doubles the SUDI risk and babies can turn onto their front.
The second myth is that sleeping on the back causes flat heads. This is not true either.
Babies’ heads change shape due to pressure on a soft skull when the head rests on the same spot. This can happen in all sleep positions because babies have heavy heads and sleep a lot.
A flat head can be avoided by varying the resting spot of the head and having plenty of upright time and tummy time when a baby is awake. It is false protection to avoid sleeping babies on the back as a way to prevent flat heads.