Silicones: Dimethicone, Cyclopentasiloxane and the Feel They Buy

Silicones appear in primers, foundations, sunscreens and moisturisers, and they are blamed for clogged pores and praised for a silky finish, often in the same review. The family covers a wide range of molecules, and the viscosity grade — measured in centistokes — decides the behaviour far more than the INCI name does.

1. The viscosity scale

Dimethicone at 5 to 100 cSt is a light, spreading fluid that gives slip and reduces tack. At 1,000 cSt it feels silkier and slightly slower. At 100,000 cSt and above it behaves as an occlusive that forms a barrier and can feel heavy. A product described as “silicone-heavy” is usually using a high-viscosity grade where a low one would have been better.

2. Volatile silicones

Cyclopentasiloxane and dimethicone are used as volatile carriers that evaporate after application and leave a dry, powdery finish. That is the mechanism behind many primers and long-wear foundations. Regulatory pressure on some cyclosiloxanes in the EU has pushed formulators toward alternatives, so a formula built five years ago may need a substitution.

3. Feel engineering

Silicones reduce the tack of glycerin, improve the spread of a pigment dispersion, and give a smooth, even application. A foundation without silicone needs more emulsifier and more powder to achieve the same feel, and it usually ends up heavier. The trade is real and rarely absolute.

4. Comedogenicity

Dimethicone is rated low on comedogenicity scales and is used in products for acne-prone skin. The reputation comes from heavy occlusive grades in poorly removed makeup, not from the molecule itself. A cleanser that removes the product properly resolves most of the complaint.

5. Silicone in sunscreen

Silicone improves the spread of a mineral filter and reduces the white cast by helping the particles align evenly. It also improves water resistance. A mineral sunscreen with 5 percent dimethicone feels noticeably better than the same formula without it.

6. Substitution pressure

Some markets restrict specific cyclosiloxanes, and brands with sustainability commitments are reformulating away from silicones. The alternatives — esters, plant oils, volatile hydrocarbons — behave differently, and a drop-in substitution usually changes the texture. Plan a sensory panel with the substitution rather than assuming equivalence.

7. Testing the claim

Non-comedogenic claims need a human panel, not an ingredient rating. A product with dimethicone can still be non-comedogenic if the panel confirms it, and a product without silicone can still clog pores. The claim belongs to the finished formula.

8. Wear on oily lids

On an oily lid a silicone-based primer holds pigment longer than a water-based one, because the film resists the oil that dissolves most binders. The trade-off is that the primer itself must be removed with an oil cleanser, or the residue builds up and the lid becomes more textured over time. Instruct a double cleanse and the complaint disappears.

9. Silicone and the ingredient list

The INCI panel lists dimethicone, dimethicone crosspolymer, cyclopentasiloxane and similar names, and consumers increasingly read them as a warning. A brand can reduce the visible list by using lower-viscosity grades at lower doses without losing the feel, or by switching to an ester system and accepting a slightly different texture. Either way the decision should be made on a sensory panel, not on perception data alone.

10. Where it fits

Silicones appear across the primer and setting spray range; the texture question continues in the texture entry.