Silicones in Skincare Formulation: The Volatile-to-Elastomer Chemistry, Occlusion Science and the 2026 Evidence

Melasyl Skin Tech Lab — Formula Science

Ask ten formulators whether silicones belong in a brightening serum and you will get ten different answers. The disagreement is almost always a category error: “silicone” is not an ingredient but a polymer family whose behaviour is set entirely by chain length, volatility and side-group chemistry. Get those three variables right and silicones become one of the most useful tools in a formulator’s toolkit; get them wrong and you build a film that either blocks your actives or collapses on the shelf.

What “silicone” actually means in an INCI list

Nearly every cosmetic silicone is a polydimethylsiloxane (PDMS) built from repeating −Si(CH₃)₂−O− units. The repeat number n determines viscosity: from 0.65 cSt hexamethyldisiloxane (n = 0) through low-viscosity linear fluids to gum-grade polymers above one million cSt. Because PDMS surface tension sits near 20–21 mN/m versus roughly 72 mN/m for water, silicones spread readily, level films and resist greasy drag — the physical origin of the “dry-touch” feel (Noll, Chemistry and Technology of Silicones, 1968).

Three architectural families matter in practice. Volatile methylsiloxanes — cyclopentasiloxane (D5), cyclohexasiloxane (D6) and low-molecular-weight linear fluids — evaporate after application. Non-volatile dimethicones stay on skin and form films. Functional silicones — dimethiconol (hydroxyl-terminated), cetyl dimethicone, PEG/PPG-dimethicone and amodimethicone — carry side groups that change solubility, emulsification or substantivity.

Volatile silicones: the “dry” carrier

Volatile silicones are best understood as transient solvents. They dissolve lipophilic actives, spread easily, then evaporate over minutes, leaving the dissolved active concentrated at the skin surface. This is why anhydrous serums, silicone-based sunscreens and long-wear foundations feel weightless. The trade-off is regulatory: Commission Regulation (EU) 2018/35 restricted D4 and D5 to below 0.1% in rinse-off cosmetics from January 2020, and D6 restrictions have since extended into leave-on categories — a real constraint for any brand selling into the EU.

Non-volatile dimethicone: the occlusive film

High-molecular-weight dimethicone deposits a continuous, breathable film that lowers transepidermal water loss (TEWL) and supports barrier recovery. Silicone gel sheeting, whose clinical mechanism is essentially an occlusive dimethicone film, is one of the better-evidenced adjuncts in scar management (Mustoe, Aesthetic Plast Surg, 2008; O’Brien & Pandit, Cochrane Database Syst Rev, 2006). In leave-on skincare the same property cuts both ways: reducing TEWL is beneficial, but a heavy occlusive layer can slow the partitioning of hydrophilic brightening actives — niacinamide, arbutin, tranexamic acid — out of the vehicle and into the stratum corneum. The film helps water retention and can hinder water-soluble penetration.

Elastomer gels: structure without a thickener

Cross-linked silicones — dimethicone crosspolymer and dimethicone/vinyl dimethicone crosspolymer — swelled in a volatile carrier produce shear-thinning elastomer gels. These gels suspend pigments, mineral UV filters and resorcinyl actives without settling, then melt under finger shear for a cushiony, non-tacky feel. Critically, they thicken independently of pH and electrolytes, so a formulator can run an L-ascorbic acid serum at pH 3 or an azelaic acid system without the carbomer collapse that plagues charged thickeners. For suspension-heavy formulas, this is the single most useful silicone capability.

Do silicones cause breakouts or “suffocate” skin?

Dimethicone itself carries a low comedogenic rating, and the “silicone suffocates skin” claim overstates the case: PDMS films are gas-permeable and do not create a hermetic seal. The more defensible criticism is accumulation — layering multiple occlusive silicones with petrolatum and heavy esters can trap sebum in acne-prone skin. The fix is formulation discipline, not elimination: pair a volatile carrier with a single functional dimethicone rather than stacking films.

Matching silicone architecture to the active

• Low-pH vitamin C: an anhydrous or volatile-silicone vehicle limits water-driven oxidation and extends L-ascorbic acid stability, with the volatile carrier concentrating the active on dry-down.
• Hydrophilic brighteners (niacinamide, arbutin, TXA): keep the non-volatile occlusive load low so partitioning into the stratum corneum is not throttled; use volatiles for spread, not occlusion.
• Resorcinyl and pigment-suspension formulas: an elastomer gel suspends particles and delivers even coverage with no electrolyte sensitivity.
• Barrier and post-procedure: a mid- to high-viscosity dimethicone or dimethiconol film for TEWL control where penetration speed is secondary.

A practical silicone formulation protocol

1. Choose volatility first. Decide whether the silicone is a transient carrier (volatile) or a permanent film (non-volatile); this single choice sets dry-down, tack and penetration behaviour.
2. Add structure with an elastomer. Use a 20–40% crosspolymer gel for suspension and sensory cushion, adjusting until the gel no longer flows at rest.
3. Rebalance emollients. Silicones are poor emollients on their own; combine with esters or vegetable oils for flexibility and after-feel.
4. Test active partitioning. Run an in-vitro release or Franz-cell study when hydrophilic actives sit under a non-volatile film.
5. Confirm compatibility and stability. Verify that the silicone does not interfere with the preservative system and check for phase separation across freeze-thaw cycles.

Bottom line

Silicones are neither hero nor villain — they are architecture. Volatile fluids concentrate actives and vanish; dimethicones occlude and protect; elastomer gels build structure that ignores pH. The formulator’s job is to read the active first and then select the silicone that carries it, not to pick a silicone and hope the active survives. For brightening formulas in particular, the right volatile-plus-elastomer combination delivers elegant texture without sacrificing penetration — which is exactly where most silicone criticism originates.