Dimethicone: Notifying the Most Common Cosmetic Silicone

If you have ever filed a Cosmetic Notification Form for a primer, a hair serum, or a lightweight moisturizer, there is a decent chance dimethicone was on your ingredient list. It is one of the most widely used ingredients in the entire cosmetics industry, and precisely because it is so common, it is also one of the ingredients makers get sloppy about when it comes time to fill in the actual CNF fields.

What dimethicone is doing in your formula

Dimethicone is a silicone polymer. Its job on the skin or hair is mostly about feel and finish. It smooths, it fills in surface irregularities so hair looks less frizzy and skin looks less textured, and it forms a light, breathable film that gives products that silky, fast-absorbing slip cosmetic chemists call "sensory glide." Some grades also act as anti-foaming agents in liquid formulations, which is why you will occasionally see it in tiny amounts in products where foam control matters more than skin feel, like certain liquid soaps or shampoos.

The INCI name and the CAS number

The INCI name is simply Dimethicone, straightforward and consistent across suppliers. The CAS registry number most commonly associated with it is 9006-65-9. Here is a wrinkle worth knowing: dimethicone is a polymer, and polymers often exist across a range of molecular weights and viscosities, all sold under the same INCI name. A 350 cSt dimethicone and a 12,500 cSt dimethicone are chemically the same substance in the eyes of INCI nomenclature, just different viscosity grades, and both should map to the same CAS number and same INCI listing on your notification.

Viscosity grades and why they matter to you, not to the CNF

The viscosity grade (measured in centistokes, cSt) is a formulation decision, not a regulatory one. Lighter grades, in the 5 to 350 cSt range, spread thin and fast, good for facial products where a heavy film would feel greasy. Heavier grades, into the thousands or tens of thousands of cSt, sit longer on the surface and are common in hair serums where you want more visible shine and frizz control.

For notification purposes, what matters is that you are listing dimethicone by its correct INCI name and reporting its actual concentration in the finished product, not the concentration of a supplier blend it might be part of. This is the detail that trips people up most.

Blends are where the math goes wrong

Dimethicone rarely arrives at your bench as pure dimethicone. It is frequently pre-blended by suppliers into carrier systems, cyclomethicone-dimethicone blends, or silicone elastomer gels, sold under a trade name. That trade name never appears on your filing. You need to break the blend into its INCI components and calculate the real percentage of dimethicone in your finished product by multiplying the blend's use level in your formula by the proportion of dimethicone inside that blend.

Scenario	Calculation
You add 2% of a supplier blend that is 50% dimethicone	2% x 0.50 = 1.0% dimethicone in finished product
You add 0.5% pure dimethicone directly	0.5% dimethicone in finished product, no further math needed
Blend contains dimethicone plus cyclopentasiloxane	Report both INCI names separately, each at its own calculated percentage

A quick summary table for the CNF

Field	What to enter
INCI name	Dimethicone
CAS number	9006-65-9
Typical function	Skin conditioning, hair conditioning, anti-foaming
Hotlist restriction	None currently specific to dimethicone itself; always check the current Cosmetic Ingredient Hotlist before filing
Concentration	Calculated actual percentage in finished product, not blend use level

Always confirm against the current Cosmetic Ingredient Hotlist before you file, since Hotlist entries and restricted concentration limits do get updated, and a guide like this one is a starting point, not a substitute for checking the live list at notification time.

Because dimethicone shows up buried inside so many supplier blends, it is one of the ingredients Cosmetic Comply's matching engine is built to catch automatically, expanding the blend, carrying the percentage math through, and mapping it to the right INCI and CAS before it ever reaches your CNF submission.