Cyclotetrasiloxane

Cyclotetrasiloxane (D4) is a cyclic silicone with four siloxane units. CAS number 556-67-2. Historically used as a volatile carrier in personal care products. Regulatory note: D4 is SVHC-listed under EU REACH at lower thresholds than D5. Most modern cosmetic formulations have eliminated D4. NISHKA does not produce D4 as a standalone product, but trace D4 may appear as an impurity in some cyclic silicone grades — always specify acceptable limits at the brief stage.