Silicones have many different forms and are used widely in the medical field for wound healing, burn healing, and bandage material) for cosmetics(in liquid foundation), and hair products(leave in shine products).
I'm finding my clients, and estheticians don't have a lot of information on silicone based ingredients so I'm here to provide you with a little back information.
Silicone is derived from Silica, a type of sand, commonly used as a physical bead exfoliant in skincare. Forms are also in more of a soft gel/clear light weight cream texture in foundation, acne treatments, and barrier creams. It's most common forms in skincare and cosmetics are listed in the ingredients as phenyltrimethicone, cylohexasiloxane, cyclopensiloxane, and dimethicone.
Silicones are large molecules that cannot penetrate the skin due to its size, however, in make-up this is a positive. Silicones are often used in a liquid/gel form in liquid foundations to help foundation to smooth over the skin evenly, and because it doesn't penetrate the skin and its hydrous properties evaporate quickly, foundation stays put on the skin longer and doesn't travel around your complexion.
In skincare silicones are used in BB creams so product goes on thicker for more tint coverage but feels very light, and is also used in barrier creams for sensitive skin, or in acne treatments. Its benefits in barrier products are that its light to the touch, softens the skin, doesn't penetrate skin so it will provideall day physical protection for skin. This way wind won't come into direct contact with a compromised lipid barrier of skin(skin can become very dehydrated when exposed to cold winds). Silicones are very porous as well, so skin can still function normally under it, without blocking pores, or ostia.
In acne skincare silicones are widely used. The light texture, the skin softening benefits, and porous tendencies allow deep penetrating small molecules of active ingredients to penetrate and treat acne, while protecting and keeping irritants off the skin helping greatly with clients suffering from acne. Silicones also have a mattifying effect on the skin.
There is controversy surrounding silicones worsen acne. I've researched this extensively and have come to the conclusion that silicones are used in the medical field as wound dressing, burn healing and wound healing because silicones have less irritation risk than other options. Burns need oxygen exposure to heal, and acne bacteria (propionibacterium acnes) dies when coming into contact with oxygen, demonstrating that silicones are "breatheable". Making it an excellent ingredient for acne products. Also because silicones are so porous and are too large to block or penetrate ostia and skin functions so well through it, its highly unlikely they cause worsening of acne conditions, but there are few studies done on this topic, for me to source as a reference.
To read more on silicones in the beauty industry, and in the medical field check out the following links: