Cyclomethicone

Overview

Cyclomethicone is the umbrella name for a family of cyclic (ring-shaped) silicones, the most common being cyclopentasiloxane (D5) and cyclotetrasiloxane (D4). It is a clear, water-thin, nearly odourless fluid that feels dramatically slippery for the first few seconds on skin and then evaporates, leaving behind essentially nothing.

That single property — wet-feel followed by a dry, powder-finished hand — is what makes it so widely used. Antiperspirant sticks, hair detangling sprays, “matte” primers, and quick-absorbing foundations all rely on cyclomethicone for that signature application feel.

A regulatory note matters here. In the EU, cyclotetrasiloxane (D4) is restricted to under 0.1% in rinse-off products and has additional restrictions in leave-on cosmetics due to environmental persistence concerns. Cyclopentasiloxane (D5) is also restricted in rinse-off products to under 0.1%. For leave-on products, D5 remains permitted but is on the watchlist. The US has fewer restrictions. Many suppliers now sell “non-cyclic dimethicone” alternatives (like hexamethyldisiloxane, isododecane, or cyclomethicone-free volatile silicones) for makers who want to avoid the regulatory risk.

Shelf life is indefinite if the bottle is kept closed. Once open, the volatility means you will lose product to evaporation if you do not seal it tight.

What it does in a formula

Cyclomethicone is a volatile carrier. It dissolves other silicones (and some oils), helps them spread thinly across skin or hair, then evaporates within 30-60 seconds, leaving the cargo behind without any silicone “weight.” This is exactly the function you want in:

• Antiperspirant sticks (carries the aluminium salt and dries fast)
• Hair smoothing serums (delivers heavy dimethicone evenly without greasy feel)
• Sunscreen sprays (helps the active ingredients sheet across skin)
• Setting sprays and primers (instant slip, then matte hand)

It does not condition, moisturise, or otherwise persist on skin. Whatever skin-feel benefit you experience comes from what it carries.

How to use

Add to the cool-down phase, below 40 C. Cyclomethicone is too volatile to heat — you will boil off significant product above 50 C.

For pouring into a stick or solid base, blend cool, fill cool, and let it set at room temperature. For sprays, the cyclomethicone often makes up 30-70% of the formula and provides the entire “delivery vehicle.”

Usage rates by product type:

• Antiperspirant and deodorant sticks: 15-40%
• Hair serums (leave-on): 30-70% as carrier; the rest is heavier dimethicones
• Primers and makeup vehicles: 5-20%
• Sunscreen vehicle: 5-15%
• Quick-absorbing body oils: 5-30%
• Setting sprays: 3-10%

It pairs naturally with heavier silicones — typically 60-70% cyclomethicone with 30-40% dimethicone 100-350 in a hair serum, for example.

Best for / Worst for

Best for: antiperspirant and deodorant sticks, makeup primers, hair smoothing serums, quick-drying body oils, sunscreen spray vehicles, products where you want maximum slip with zero residue.

Worst for: EU-compliant rinse-off products (the 0.1% limit makes it essentially unusable), brands marketing to environmentally conscious customers (the persistence story is real and worth taking seriously), anyone wanting a moisturising or long-wear effect (cyclomethicone evaporates and leaves nothing behind).

Common pitfalls

Treating it as a moisturiser. It is not. It is a delivery vehicle. If your formula relies on cyclomethicone for skin-feel and you remove it, you will get back a sticky base. Plan for that when reformulating.

Heating it. A 70-75 C emulsification cycle will boil off 20-40% of your cyclomethicone. Always add it during cool-down, ideally below 40 C, and stir gently.

Ignoring regulatory direction. If you sell into the EU, cyclomethicone in rinse-off products at any significant level will land you outside the regulation. Reformulate with isododecane or a linear volatile silicone if you need the same skin-feel.

Open containers. Cyclomethicone evaporates from an open bottle within hours to days. Keep it sealed.

Substitutes

• Isododecane — non-silicone volatile, very similar skin-feel, no D4/D5 regulatory issues. The most common drop-in.
• Isohexadecane — slightly heavier feel, slower-drying, still volatile.
• Hexamethyldisiloxane (HMDS) — a different volatile silicone, not on the cyclic watchlist.
• Light, fast-absorbing esters (like coco-caprylate or isoamyl laurate) — give you some slip without the volatility, but you lose the dry-down finish.
• Ethanol — the classic volatile carrier in setting sprays and some antiperspirants. Drying on skin.