Smashbox Photo Finish Primer contains silicones like Cyclopentasiloxane and Dimethicone that create a barrier between skin and makeup or skin and the environment.

Recently, a friend cited an article she’d read that said makeup primer kept bacteria from getting into your pores. Can this be true? I though. Well, let’s look at the facts. For the purposes of this post, I focused on liquid primers, such as Smashbox Photo Finish Primer ($38, smashbox.com) because there are many kinds of primers and many ingredients.

However, liquid primers generally contain silicone for ease of spreading, as well as polymers and waxes.

[Read More: Are BB Creams Worth It? Which is the Best?]

What is Makeup Primer?

Makeup primer helps makeup go on and stay on better.

Primer is a product that helps to even out skin and allow makeup to stay on better. Many of them are silicone-based. Silicone primer seals in your moisturizer and keeps the oil in your skin from affecting your foundation, essentially by creating a barrier. It also stops your foundation from slipping into fine lines (Makeup Makeovers Beauty Bible).

Cosmetics companies have included silicone, for it’s emollient properties, in skin care since the 1950s (Cosmetics and Toiletries). Particularly in makeup, silicones brought easier spreading and allowed for formulas that use light interplay to help soften the focus of wrinkles. In addition to this, silicones can help absorb excess oil, keeping makeup fresh throughout the day.

Explain the Barrier Makeup Primer Creates

Silicone is a light occlusive agent, meaning that it helps to seal in moisture, preventing water loss, but also helps to create something of a barrier between skin and the environment (The Chemistry and Manufacture of Cosmetics).

But silicones’ structure is quite different in that it’s made up of larger molecules with wider spaces between each molecule. This means that silicone is quite breathable and explains why it doesn’t feel heavy.

This structure means that while silicone can help prevent water loss, it doesn’t clog pores. It’s still important though with occlusive agents that you have clean skin (you can use skin care underneath, of course) before applying, lest you trap irritating agents.

So does it Protect Against Bacteria?

In the same way silicone-based barrier creams can protect against contaminants, silicone-based primers can protect skin.

While silicones may have been used in cosmetic formulas originally for their ease in spreading and moisture, they may have other benefits as well. Silicones are often used in what are called “barrier creams.” These are creams used in athletic, medical, industrial, etc. use to prevent certain bacteria, skin irritants, etc. (The Royal Society of Medicine).

When they were first looking at silicone-based medical barrier creams in 1956, a test comparing silicone barrier cream to the traditional method found that silicone barrier cream worked equally as well with less potential for irritation at prevent bedsores (British Medical Journal).

Barrier creams efficacy is well documented for protecting skin from irritants. Though, they don’t protect from everything, for example, they may not be effective against corrosive agents (Journal of Investigative Dermatology). They can also exacerbate skin irritation if they’re used on already diseased skin or with irritating ingredients.

Bottom Line

Primers are useful for the application of makeup because they can help makeup go on more smoothly, stay on, absorb excess sebum, and stop reactions between oils and makeup. They create a breathable barrier between skin and environment. There is discussion that they may also stop makeup from getting into pores and stop bacteria as well. Barrier creams containing silicone have been shown to help stop contaminants from going into the skin and products like Smashbox Photo Finish Primer have one of the heaviest silicones, dimethicone. So, the bottom line is that makeup primers may help stop bacteria from getting into the skin.