Dimethicone

What it is

Dimethicone is a synthetic silicone polymer built from repeating silicon-oxygen units, made from silica (sand) rather than petroleum. Its molecules are too large to pass through the outer layer of skin, so it stays on the surface. Formulators use it because it spreads easily, cancels the greasy feel of oils, and forms a thin flexible film that slows water loss without feeling heavy.

What it does well

• Reduces water loss from the skin surface without truly sealing it

  In a controlled comparison of silicone-based and silicone-free emulsions, the silicone versions produced transepidermal water loss values comparable to untreated control skin, meaning they smooth and protect without behaving like an occlusive wax.

  Moderate evidence

• Improves texture and reduces the greasy feel of rich formulas

  In the same in vivo comparison, volunteers scored the silicone-containing emulsions higher for silkiness, freshness and softness and lower for greasiness, with no irritation recorded.

  Strong evidence

• Does not clog pores in the way the popular claim suggests

  The idea that silicones 'suffocate' skin or trap debris in pores is not supported by testing: dimethicone is chemically inert, is not metabolised by skin bacteria, and silicone emulsions did not produce occlusion in vivo. Comedogenicity data that circulate online often come from the rabbit-ear assay, which is known to over-predict reactions in human skin.

  Moderate evidence

Worth knowing

• Can feel like build-up if a product is not properly cleansed off

  Dimethicone is water-repellent, so a light cleanser may leave a residue that feels slick. A normal surfactant cleanser removes it; this is a texture issue, not a safety one.

  Matters most toPeople who use very rich silicone-heavy products and only rinse with water.

Where the EU stands

Sources (2)

Every link goes to the original: a journal, a PubMed record or an EU document.

1. [1]
   A comparison between silicone-free and silicone-based emulsions: Technological features and in vivo evaluation

   International Journal of Cosmetic Science · 2022 · doi:10.1111/ics.12800

   Silicone-based emulsions were stable, non-irritating and did not cause skin occlusion, with transepidermal water loss comparable to control skin.

2. [2]
   Analysis of comedone, sebum and porphyrin on the face and body for comedogenicity assay

   Skin Research and Technology · 2016 · doi:10.1111/srt.12244

   Human facial and back testing gives more reliable comedogenicity results than the rabbit-ear model, which over-reacts to materials that do not cause comedones in people.