Understanding Dimethicone: A Dual-Action Polymer
Dimethicone is a synthetic silicone-based polymer, also known as polydimethylsiloxane (PDMS) [1.3.2]. Its large molecular weight means it primarily sits on the surface of the skin rather than being absorbed, a key factor in its safety profile [1.3.4, 1.4.2]. In pharmacology, dimethicone has two primary, yet distinct, applications: as a topical skin protectant and as an internal antiflatulent (often as its activated form, simethicone).
As a skin protectant, the U.S. Food and Drug Administration (FDA) has approved its use in over-the-counter (OTC) products at concentrations between 1% and 30% [1.9.1]. It is widely regarded as a safe and effective ingredient by regulatory bodies like the FDA and the Cosmetic Ingredient Review (CIR) Expert Panel [1.9.2, 1.9.4].
How Dimethicone Works on the Skin
When applied topically, dimethicone leverages its unique molecular structure to provide several benefits for the skin [1.4.2, 1.6.4]:
- Forms a Protective Barrier: It creates a permeable, breathable film over the skin's surface. This barrier performs two main functions: it protects the skin from external irritants like allergens, pollutants, and friction, and it reduces transepidermal water loss (TEWL) by sealing in moisture [1.4.4, 1.6.2].
- Acts as an Emollient: Dimethicone fills in the microscopic gaps between skin cells, which smooths the skin's surface and improves its softness and flexibility. This gives products containing it a characteristic silky, non-greasy "slip" [1.4.1, 1.4.3].
- Improves Product Texture and Application: In cosmetic and skincare formulations, it enhances spreadability, allowing for a more uniform application of other ingredients, such as the physical filters in sunscreens [1.4.2]. It also gives products a lightweight, matte finish [1.4.4].
- Aids in Scar Management: Silicone gels and sheets, which are primarily composed of dimethicone, have been shown to be effective in reducing the texture, color, and height of hypertrophic scars and keloids. The hydrating and protective environment it creates is believed to regulate collagen deposition during the healing process [1.4.2, 1.6.2].
Internal Use: Dimethicone as an Antiflatulent
Internally, dimethicone (as simethicone) works as a carminative and antifoaming agent to relieve symptoms of gas and bloating [1.3.2]. It does not prevent the formation of gas but works mechanically in the digestive tract. It lowers the surface tension of gas bubbles, causing them to coalesce into larger bubbles that are more easily passed from the body through belching or flatulence [1.3.2]. It is not absorbed into the bloodstream and is considered safe for internal use at recommended doses, even during pregnancy and breastfeeding [1.9.2].
Is Dimethicone Safe for Your Body?
For the vast majority of people, dimethicone is considered extremely safe for both topical and internal use [1.9.2]. Its large molecules prevent skin penetration, eliminating the risk of systemic toxicity from topical application [1.4.2]. Multiple safety assessments, including those by the CIR Expert Panel, have concluded it is non-toxic and not a carcinogen [1.4.1, 1.9.4].
One of the most common concerns is whether it clogs pores (comedogenicity). Scientific consensus and dermatological sources state that dimethicone is non-comedogenic, meaning it does not clog pores [1.10.1, 1.10.2, 1.10.3]. The breathable barrier it forms allows for the normal passage of substances like sweat and sebum [1.6.3]. However, some sources suggest its occlusive nature could potentially trap dirt and oil already on the skin if not cleansed properly, which might be a concern for acne-prone individuals [1.2.1].
Potential side effects are rare but can include [1.5.3, 1.5.1]:
- Mild skin irritation, itching, or redness.
- A feeling of dryness if it over-absorbs surface oils on very dry skin types [1.2.1].
- Allergic reactions, though uncommon, can manifest as hives, swelling, or difficulty breathing and require immediate medical attention [1.5.1].
Dimethicone vs. Other Common Ingredients
A comparison helps to contextualize dimethicone's role in skincare.
| Feature | Dimethicone | Petrolatum | Hyaluronic Acid |
|---|---|---|---|
| Primary Function | Skin protectant, emollient, occlusive [1.4.3, 1.6.4] | Highly occlusive, skin protectant [1.8.4] | Humectant (draws water into skin) [1.7.1, 1.7.2] |
| Texture & Feel | Silky, smooth, non-greasy, matte finish [1.2.1, 1.8.1] | Greasy, heavy feel [1.8.1] | Can be tacky, but generally lightweight in formulations |
| Origin | Synthetic (derived from silica) [1.4.1, 1.8.3] | By-product of petroleum refining [1.8.3] | Can be synthetic or derived from bio-fermentation [1.7.4] |
| Pore Clogging? | No (non-comedogenic) [1.10.2] | No (non-comedogenic) [1.8.2] | No (non-comedogenic) |
| Mechanism | Forms a breathable barrier to lock in moisture [1.6.2] | Forms a strong barrier that is less breathable [1.8.2] | Binds to water, hydrating the skin from within [1.7.2] |
Environmental Considerations
While considered safe for human health, there are growing concerns about the environmental impact of silicones like dimethicone [1.11.3]. Because they are not readily biodegradable, they can accumulate in aquatic ecosystems after being washed down the drain [1.11.1, 1.11.4]. Scientists have found silicones in the blood of various animals, and some organizations express concern that they may be toxic to these ecosystems [1.11.1]. This environmental footprint is a key reason some consumers and brands are seeking silicone-free alternatives [1.11.2].
Conclusion
In summary, what dimethicone does to your body depends on its use. Topically, it is a safe and effective skin protectant and emollient that smooths skin, locks in moisture, and improves the texture of cosmetics without clogging pores. Internally, it is a safe and effective agent for relieving gas and bloating. While side effects and allergic reactions are rare, they can occur. The primary controversy surrounding dimethicone is not related to human health but to its environmental persistence.
