Silicones in skin care: villain or misunderstood?

Rub a modern moisturizer between your fingers and notice how it glides: that’s usually a silicone at work. Dimethicone and its relatives are in primers, sunscreens, hair conditioners, diaper creams and half the lotions in the pharmacy, and they’ve picked up a reputation for “suffocating” skin along the way. The evidence tells a calmer story. Here’s what silicones do, what the safety reviews say, and why avoiding them is a preference rather than a precaution.

What are silicones, and what do they do in a product?

Silicones are synthetic polymers, long chains built from silicon and oxygen atoms with small carbon groups attached. On an ingredient list they end in “-methicone” or “-siloxane”: dimethicone, cyclopentasiloxane, dimethiconol, cetyl dimethicone, and so on.

In a cream they do three jobs:

• Slip. Silicones spread with almost no drag, which is why a silicone-based product glides on and feels silky rather than sticky.
• Smoothing. They fill in the microscopic roughness of the skin surface, which is what gives a primer its “blurring” effect and a conditioner its detangling power.
• Protection. They leave a thin, flexible film that sits on top of the skin and shields it from friction and irritants.

The film is the part that matters for dry or damaged skin. In the US, dimethicone is one of a short list of approved skin-protectant active ingredients: the FDA’s over-the-counter monograph allows it at 1 to 30% in products labelled to “temporarily protect” chapped or cracked skin and minor cuts, scrapes and burns. That’s the same category as petrolatum and zinc oxide, the classic diaper-rash and barrier ingredients.

What the safety reviews found

Silicones are big molecules, and big molecules don’t get through skin easily. The Expert Panel for Cosmetic Ingredient Safety (the independent panel that reviews cosmetic ingredients in the US) re-examined dimethicone and 29 related polymers in 2022. Its conclusion: they’re safe in cosmetics “in the present practices of use and concentration” when formulated to be non-irritating.

The details behind that verdict are reassuring. In animal studies dimethicone was rated a minimal irritant at concentrations from 5% to 100%. It wasn’t a sensitizer (an ingredient that can teach the immune system to react) in four animal assays, nor in a human repeat-insult patch test on 83 volunteers, the standard test where a substance is applied over and over to see whether allergy develops. In feeding studies it passed through without being absorbed.

The one gap the panel flagged has nothing to do with skin: it said the data were insufficient to judge products applied by airbrush, where fine droplets might be inhaled. For a cream you rub on, that’s not a concern.

Allergy to dimethicone is rare. If you break out from a silicone-based product, the fragrance, preservative or sunscreen filter in it is a far more likely explanation.

The “suffocating skin” myth

The idea that silicones form an airtight seal and trap sweat, bacteria and oil comes from confusing them with true occlusives. An occlusive is an ingredient that blocks water from evaporating off the skin; petrolatum is the textbook example.

A 2014 study in Skin Pharmacology and Physiology tested exactly this. Researchers compared a petrolatum cream with creams containing three silicones (dimethicone, dimethiconol and a dimethicone crosspolymer) and measured transepidermal water loss, the amount of water evaporating through the skin. Petrolatum cut water loss sharply and kept it down for more than four hours. The silicone creams lowered it briefly at 15 minutes, but after that the readings weren’t significantly different from untreated skin. The authors’ conclusion was blunt: there’s “a clear difference” between petrolatum’s occlusion and the water-vapour permeability of common silicones.

In plain terms, the silicone film lets water vapour through. Your skin keeps doing what it does underneath it. That’s also why silicones alone aren’t a great fix for very dry skin: they protect and smooth, but they don’t lock moisture in the way an ointment does.

Do silicones cause acne?

There’s no good evidence that they do. The 2022 safety review found dimethicone minimally irritating and non-sensitizing at use concentrations, and the 2014 permeability study shows the film doesn’t seal the skin, so the “trapped oil and bacteria” explanation doesn’t hold up. If a silicone-heavy product seems to make you break out, look at the whole formula rather than the silicone, and if you’re on a prescription acne treatment, ask your pharmacist which moisturizer pairs well with it rather than stopping the treatment.

So why do some people avoid them?

Three honest reasons, none of which is “they damage skin”.

The feel

Some people find the slippery, slightly artificial finish unpleasant, or feel that a silicone-based moisturizer sits on the skin rather than sinking in. That’s a matter of taste, and there are plenty of silicone-free formulas.

Hair build-up

This one has some substance. A 2015 review of hair cosmetics in the International Journal of Trichology describes dimethicone as the most widely used silicone in hair care, valued for protecting the hair shaft from abrasion. It also notes that some silicones are hard to remove because they cling so well, and that formulators use “cationic bridging agents” to make silicones deposit even more strongly on damaged hair. If your hair feels coated and limp after weeks of the same conditioner, that’s the effect people are describing. It’s cosmetic, not harmful, and it washes out with time or a different shampoo.

The environment

The concern here is real but specific. The small, volatile cyclic siloxanes used to make products evaporate quickly, D4 and D5, were assessed by Canada under the Chemicals Management Plan. D4 was found “not harmful to human health” but “entering the environment at concentrations that may be harmful”, because it persists in air and sediment and is toxic to aquatic life. It was added to Canada’s Toxic Substances List in 2011, with controls aimed at industrial effluent; the government concluded that controls on personal care products weren’t needed.

D5 went through an unusual second look. An initial 2009 assessment flagged an environmental concern, a Board of Review examined the science at formal hearings, and in 2012 Canada concluded D5 “is not entering the environment at levels that are harmful”. Neither D4 nor D5 was found harmful to human health. If you prefer to avoid D4 anyway, look for “cyclotetrasiloxane” on the label; the large, non-volatile silicones like dimethicone weren’t the subject of these assessments.

What to take from all this

Silicones are among the best-tested and least reactive ingredients in a typical moisturizer. They make products spread well, smooth the skin and form a breathable protective film that regulators recognize as a skin protectant. They don’t suffocate skin, and allergy to them is rare.

If you skip them because you dislike the feel, because your hair builds up, or because you’d rather not use volatile siloxanes, those are fair choices. Just don’t expect “silicone-free” to mean gentler: what replaces the silicone matters more than its absence. And if a rash or breakout doesn’t settle within two weeks of changing products, see your doctor or pharmacist rather than guessing at ingredients.