Cyclotetrasiloxane

Cyclotetrasiloxane (D4) is a volatile silicone used as a slip agent/solvent in leave-on hair and skin products, often at several percent, and it is generally non-reactive and not a common cause of irritant contact dermatitis in clinical patch-testing experience. While true allergy is rare and it typically evaporates after application, a small subset of highly reactive or barrier-impaired patients can still report stinging or intolerance from occlusion/ vehicle effects in real-world routines. Given the overall very low intrinsic irritancy but acknowledging compromised-skin populations, it best fits the 'exceptionally gentle' category rather than completely inert. Safety Notes: In consumer skincare and personal care, cyclotetrasiloxane (D4) is most often encountered at trace-to-low levels (~0.1–1%) as a residual/carryover from cyclomethicone blends or silicone elastomer gels used to improve slip in creams, primers, and sunscreens. The highest OTC levels are found in anhydrous, silicone-volatile leave-on formats (e.g., silicone “dry oil”/body sprays, makeup primers, and waterless silicone serums) where cyclomethicone fluids can constitute the bulk of the formula, with D4 present at elevated proportions depending on the cyclomethicone grade and supplier; rinse-off products generally sit at the low end due to reduced need and volatility loss.