مضاد للتعرق ومزيل العرق

Silicone Fluids in Antiperspirant and Deodorant Formulations

Antiperspirant actives — primarily aluminum zirconium tetrachlorohydrex glycine complexes — must be dispersed in a carrier system that delivers them uniformly to the skin surface while minimizing the heavy, tacky residue associated with wax-based or petrolatum-based anhydrous vehicles. Silicone fluids, specifically low-viscosity polydimethylsiloxane (PDMS) and cyclic siloxanes (cyclopentasiloxane, D5 equivalent), are the industry-standard carriers for this application precisely because they solve both problems: excellent active dispersibility and a dry, invisible after-feel.

The functional distinction between antiperspirant (AP) and deodorant (DO) product formats drives different silicone selection criteria. Aerosol sprays and pump sprays tolerate very low-viscosity dimethicone (0.65–5 cSt) that atomizes cleanly without clogging nozzles. Roll-on gels and clear sticks require higher-viscosity silicone or silicone blends with gelling agents to achieve in-pack stability. Solid sticks rely on wax matrices where silicone functions as a plasticizer and spreading aid.

Functional Role of PDMS and Cyclopentasiloxane

Low-viscosity dimethicone (PDMS, 0.65–5 cSt) and cyclopentasiloxane (D5 equivalent, approximately 4 cSt) serve overlapping but distinct roles:

Cyclopentasiloxane evaporates within minutes of skin contact, leaving the aluminum salt active deposited on the eccrine gland openings without any oily residue. This volatility is the single most important functional attribute for consumer-preferred dry-feel formats. PDMS 2–5 cSt does not evaporate but provides excellent lubricity and acts as a processing aid that keeps finely milled aluminum salt particles in stable suspension in anhydrous roll-on liquids.

Formulation Considerations

Antiperspirant formulations are anhydrous by design — water would hydrolyze the aluminum active and destabilize the system. This makes silicone an ideal vehicle: it is chemically inert toward aluminum salts across the typical 12–18-month shelf life, and it is immiscible with water, so packaging integrity concerns are minimal.

Key formulation variables when incorporating ZEMSIL dimethicone into AP/DO systems:

• Active suspension stability: aluminum salt particle size must be below 10 µm to prevent sedimentation in low-viscosity silicone bases; a 1–3% suspending wax (e.g., polyethylene, C20-40 alkyl stearate) is added when PDMS viscosity is below 5 cSt
• Clarity of clear stick: cyclopentasiloxane plus a gelling copolymer (diisostearyl malate, or silicone elastomer blend such as cyclopentasiloxane/dimethicone crosspolymer) produces the optically clear gel matrix required in premium transparent sticks
• Aerosol propellant compatibility: PDMS is fully miscible with hydrocarbon propellants (isobutane/propane blends); no compatibility issue at standard 20–40% propellant levels
• Skin deposition of active: dimethicone film on skin retards moisture-triggered dissolution of the aluminum salt — this "reservoir effect" extends efficacy duration between applications

Typical loading in anhydrous roll-on: 50–70% silicone fluid (PDMS or D5 equivalent), 20–25% aluminum zirconium active, balance wax and fragrance. In compressed solid sticks, silicone loading is lower (15–30%) with the wax providing structural rigidity.

Skin Tolerance and Regulatory Status

PDMS is non-occlusive at molecular dimensions — the dimethicone film does not block oxygen or carbon dioxide exchange, distinguishing it from petrolatum occlusive films. It is non-sensitizing, non-comedogenic, and passes standard repeat insult patch testing (RIPT) without incident at the concentrations used in AP/DO. Regulatory status by region:

• EU Cosmetics Regulation (EC) No 1223/2009: PDMS (dimethicone) is a permitted ingredient; D5 (cyclopentasiloxane) is restricted in rinse-off cosmetics at >0.1% but is not restricted in leave-on products such as antiperspirants
• US FDA OTC monograph (21 CFR Part 350): silicone does not function as an approved AP active — it is classified as an inactive vehicle ingredient and requires no independent safety substantiation beyond cosmetic use
• China NMPA: listed in the Inventory of Existing Cosmetic Ingredients in China (IECIC); no leave-on restriction for PDMS or D5

Formulators specifying PDMS for European markets should confirm regional purchasing compliance around D5 for leave-on product categorization, as regulatory interpretation can vary by national competent authority.

Sourcing and Specification

ZEMSIL DM-series polydimethylsiloxane covers the viscosity range relevant to antiperspirant applications. Key grades for AP/DO:

• DM-2 and DM-5: 2 and 5 cSt low-viscosity PDMS for anhydrous roll-on and aerosol bases
• DM-10 and DM-20: plasticizer range for solid stick matrix plasticization
• DM-350: medium-viscosity anchor for silicone elastomer gel blends in clear stick formats

Purity specifications relevant to AP/DO sourcing: hydroxyl termination content (low-OH grades minimize transesterification with wax esters); D4 content (EU restricted; confirm D4 <10 ppm in D5-equivalent grades if targeting EU leave-on products); flash point (critical for aerosol manufacturing safety).

Related Reading

Silicone Oil Overview · Hair Care and Conditioning · ZEMSIL DM-Series PDMS · Silicone Emulsions for Personal Care