Namely
This substance is no longer authorized in cosmetics in Europe because it has been identified as a persistent organic pollutant (POP) or (very) persistent, (very) bioaccumulative and toxic (PBT/vPvB). Its use is prohibited by the Stockholm Convention on POPs or restricted by the REACH regulation.
-----------------------------
Cyclomethicone is a mixture of silicones D4, D5 and D6, in variable proportions. It is, like D4 and D5, suspected of being an endocrine disruptor. It is prohibited in organic products.