Almost 20 years ago prone sleeping position was established as a risk factor for sudden infant death syndrome (SIDS) and with risk reduction campaigns which largely focused on this one factor, the incidence of SIDS has declined by 50-80% in most of the countries where campaigns were conducted. However, the pathophysiological cause or causes of SIDS are not yet known, although many theories have been proposed. This paper examines several of the more controversial theories for SIDS causation. In 1997 a link between Helicobacter pylori and SIDS was proposed. Initial positive results were not confirmed. More recently there is new evidence that H. pylori may play a role in some cases but these results need to be confirmed by others. Anaphylaxis caused by milk is an older theory, which has its merits, but needs to be verified with new methods. The toxic gas theory was interesting but had flaws. “Toxic gases” have not been produced in an environment remotely resembling that found in a cot. Proponents of the theory have recommended wrapping the cot mattress in polythene to prevent the postulated gases reaching the baby, but there is no evidence that this has had any effect. The proponents have been very vocal in the lay media despite evidence that disproves this theory. No further evidence is needed for the final rejection of this theory. The harm and benefits of immunisations are a controversial topic in the lay press, although seldom in the scientific literature. As the age of infants dying from SIDS is similar to that when immunisation is given, it has been postulated that there is a causal link. Several large case-control studies have shown that immunisations are not a risk factor for SIDS and recent a Meta analysis in fact reported that immunisation halve the risk for SIDS compared with infants who had not been immunized. In conclusion, while the cause or causes of SIDS remains unknown new theories will be proposed and this is to be welcomed. These theories should be first discussed within the scientific community. Debating theories and preliminary findings in the lay media risks confusing parents of young infants and takes attention away from established risk factors and recommendations.