Silicone Use with Skin and Hair

Unmodified silicones stay on or near the surface of the skin. Not only are the molecules too big to physically enter past the upper living cells -- they associate with the upper layer of drying skin -- but they also cannot penetrate cell membranes due to their large size. They also dislike both the water and proteins inside cells.

Cyclomethicones are unmodified silicones. They evaporate quickly after helping to carry oils into the top layer of epidermis. From there, they may be absorbed by the skin. Cyclomethicones a similar function in hair care products by helping nutrients enter the hair shaft.

Dimethicones are also unmodified silicones. They form a barrier layer on the skin which must be renewed as the skin sloughs off. Dimethicones coat the surface of the hair and lubricate it, improving combing providing detangling, and thus, hair loss and breakage.

Silicones form a protective layer which helps prevent transdermal water loss -- a very useful characteristic for many products. Silicone gums provide instant shine to hair. Silicones act to help seal moisture into the hair, which helps prevent many kinds of damage.

Formulating Notes

Silicones have varying properties which affects how they are used. Their solubility in a variety of ingredients is a most important consideration. Silicones are usually blend readily with each other to provide desired properties. The solubility of silicones in other ingredients varies and must be observed when formulating.

With that in mind, here are some general rules:

You can count on unmodified silicones being insoluble in water, and other polar compounds. They will emulsify well, though, using the more common emulsifying agents.

All-silicone emulsions are possible. Silicones can be modified or changed to improve water solublity.

Silicone oils dissolve well in and will dissolve non-polar materials. These include essential oils, mineral oil, fixed oils, light esters, and sunscreen agents. Solubility decreases, however, as the size and
viscosity of the silicone increases.

Silicone gums are not soluble in fixed oils, but the carrier is. Thus the carrier dissolves, leaving the
gum as a troublesome blob.

Silicone oils are somewhat soluble in waxes, lanolin, castor oil and similar materials. The viscosity limitation is higher in these materials than it is for the fixed oils.

Silicone compounds generally have fairly low usage rates in most applications. Their usual applications include lotions, salves, conditioners and bath products that use 1 to 5 % silicone as an additive to modify "feel" and provide skin protection. Cyclomethicones are most commonly used, with the low- to medium- viscosity dimethicones. Different types of silicone may be used alone or together.

Many formulas use 2 parts cyclomethicone to 1 part dimethicone. Silicone gums are generally not usable for lotions and other emulsified products. This is due to the insolubility of the gum in fixed oils (as discussed above). It is possible to make emulsions from silicone oils only, or with mineral oil. These types of emulsions allow for the incorporation of the gums into products such as hair dressings.

Cyclomethicone may be used alone to carry essential oils in a dry oil spray -- referred to commonly as "dry perfume oil sprays". It may also be used to dilute gums to produce spray detanglers. The gum base content in a hair serum spray is usually between 5 and 10%.

* to figure CPS by comparison: H2O (water) has a viscosity of 1-5 CPS.

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