According to scientific research carried out over the last twenty years, cot mattresses are dangerous because they give off gasses which can prove fatal to babies. This apparently applies even to organic mattresses and to sheepskins because all mattresses have to be treated by law with flame retardant.
Studies have shown that conventional cot mattresses contain certain chemical compounds (phosphorous, arsenic and antimony) which react with common household fungi to create toxic nerve gases.

The effect of these gases, if absorbed into the baby’s body through the skin and lungs in sufficient quantity, is to slow down and ultimately stop the lungs from working with fatal consequences.

For more information see the following websites

www.pnc.com.au/~cafmr/sprott/

www.cotlife2000.co.nz/research.htm