Why Is Silicone in Almost Every Commercial Sunscreen Available?

Because it's inexpensive and it makes cheap formulas feel expensive.

Flip over almost any sunscreen and scan the label. If you see dimethicone, cyclopentasiloxane, cyclomethicone, dimethiconol, or anything ending in -siloxane — those are silicones. They show up two, three, sometimes four at a time in a single formula. Most people have seen them a hundred times without knowing what they are or why they're there.

Here is why they're there.

It's Cheap and It Fixes a Problem the Formula Created

High-concentration zinc oxide is difficult to work with. At the levels required for real broad-spectrum protection, the raw active is thick, resistant to spreading, and tends to sit visibly on skin. Formulators have two options: design around the problem with the right carrier ingredients, or reach for silicone.

Silicone is cheaper and faster. Dimethicone and cyclopentasiloxane are widely available, cost-effective, and solve the texture issue immediately. Customers pick up the product, feel how smooth and light it applies, and buy it again. The ingredient that made that possible never comes up.

It works well enough that most of the sunscreen industry never looked for an alternative.

What Silicone Actually Is

Silicone is a synthetic polymer. Its chemical backbone is silicon and oxygen, not carbon, which puts it in a fundamentally different category from organic ingredients. It sits chemically between rubber and plastic. It was originally engineered for industrial applications: sealants, lubricants, insulation. Personal care use came later, when the cosmetics industry recognized how useful that smooth, frictionless surface feel could be.

The two most common forms in sunscreen are dimethicone, a long-chain non-volatile silicone that stays on the skin surface, and cyclic silicones like D4 and D5, which are volatile and evaporate after application. Both create the slip and light feel that makes high-zinc formulas easier to apply.

Where It Goes After You Apply It

This is where the profit calculus gets more complicated.

Silicone is not biodegradable in any meaningful biological sense. Its silicon-oxygen backbone cannot be broken down by microorganisms. Standard biodegradation tests measure how well microbes oxidize carbon. Silicone does not have that carbon structure. It does not break down. It accumulates.

Degradation estimates range from 400 to 500 years depending on the environment. The cyclic silicones D4 and D5 have received specific regulatory attention. The European Union classifies both as very persistent and very bioaccumulative substances. Wash-off personal care products account for roughly 95% of D5 emissions into surface water in Europe. The silicone leaves your skin, enters the water system, and builds up in sediment and aquatic organisms because nothing in the environment has a pathway to process it.

This is not a dramatic or fast-moving problem. It is a slow, structural one. And it is a direct consequence of choosing cheap synthetic texture agents over alternatives that actually break down.

What It Does on Skin for Some People

For most skin types, topical silicone is uneventful. Clinical studies rate dimethicone as non-comedogenic. It does not chemically block pores.

But dimethicone is occlusive and it stays on the skin surface. For people with reactive, congested, or acne-prone skin, that film creates a layer that traps sebum and other formula ingredients against the skin. The silicone is not the direct cause. The problem is what cannot escape from beneath it.

There is also a pilling issue that gets explained away as a technique problem. Silicone-based layers do not bond with zinc oxide powder suspensions. If you apply a silicone moisturizer before a mineral sunscreen, the zinc sits on top of the silicone layer and rolls off. No amount of waiting between steps fully resolves a formulation incompatibility.

What Replaces It

Coco caprylate/caprate is one of Swellies' five ingredients. It is a plant-derived ester made from coconut oil and caprylic/capric acid. It is the primary carrier in the formula.

It does what silicone does. It is lightweight, spreads easily, and does not leave a greasy or heavy feel on skin. It is also non-comedogenic and fully biodegradable. Microorganisms can break it down. It does not accumulate in sediment. It does not persist in waterways.

It cost more to develop around than silicone would have. That was a deliberate choice.

Swellies has five ingredients. Coco caprylate/caprate is one of them because it handles the carrier and texture job that most formulas hand to silicone, without the 400-year persistence, without the film, and without the pilling risk. It was hired because it actually works, not because it covers for something else.

None of the five ingredients are workarounds. That is the point of having five.

P.S. Commercial silicones have been in production since the 1940s. They do not biodegrade. Some break down slowly through light and water over decades — but microorganisms cannot process them. What goes down the drain accumulates. The EU banned the most persistent forms from rinse-off products in 2020 for the same reason microbeads were banned in the US in 2017. Different ingredient, same problem.

No silicones. Five ingredients, all disclosed. See Swellies →