What Is C30-45 Alkyldimethylsilyl Polypropylsilsesquioxane?
C30-45 Alkyldimethylsilyl Polypropylsilsesquioxane is a silicone-based material made up of long chains of carbon atoms linked to siloxane (silicon-oxygen) units. The “C30-45” part tells us its carbon chain length sits between 30 and 45 atoms, which helps it form a flexible wear-resistant film on skin or hair. It is created through a process called hydrolytic condensation where smaller silicone building blocks are reacted with alkyl groups, then carefully blended to reach the desired chain length and texture.
This ingredient entered cosmetic labs in the early 2000s when formulators looked for lighter, more breathable alternatives to heavy waxes and oils. Its ability to lay down an invisible film without feeling sticky made it popular in both skincare and color cosmetics.
Today you will spot C30-45 Alkyldimethylsilyl Polypropylsilsesquioxane in primers, foundations, long-wear lip products, sunscreens, setting sprays, mascaras, leave-on hair treatments, moisturizers and even some sheet mask essences. Whenever brands need a smooth touch plus staying power, this silicone shows up on the ingredient list.
C30-45 Alkyldimethylsilyl Polypropylsilsesquioxane’s Cosmetic Benefits/Uses
This ingredient is prized for one main job that can make a big difference in how a product feels and performs.
- Film forming: It creates a thin flexible layer on skin or hair that locks in moisture, improves spreadability, boosts water and smudge resistance and helps active ingredients stay in place longer. The result is makeup that lasts, sunscreen that clings through sweat and skincare that keeps working between applications.
Who Can Use C30-45 Alkyldimethylsilyl Polypropylsilsesquioxane
This silicone suits most skin types including dry, normal, combination and oily because it forms a breathable lightweight film that does not usually clog pores or feel greasy. Sensitive skin generally tolerates it well thanks to its inert nature, though anyone highly reactive to silicones should watch for discomfort.
The ingredient is produced synthetically from mineral sources so it contains no animal derived substances, making it acceptable for vegans and vegetarians. Cruelty free status depends on the finished brand’s testing policies rather than the molecule itself.
Current safety data shows no systemic absorption, so products containing this material are considered low risk for pregnant or breastfeeding women. This is not medical advice, and anyone who is pregnant or nursing should check with their healthcare provider before adding new skincare to their routine.
C30-45 Alkyldimethylsilyl Polypropylsilsesquioxane does not increase photosensitivity and can actually help stabilize sunscreen films. It is also odorless and colorless so it rarely interferes with fragrance or dye sensitivities.
Potential Side Effects/Adverse Reactions
Responses to topical C30-45 Alkyldimethylsilyl Polypropylsilsesquioxane vary from one person to another. The following is a list of potential side effects that might occur, although most users will never notice any of them if the product has been formulated and used correctly.
- Mild skin irritation – stinging or redness can appear on very reactive skin types
- Allergic contact dermatitis – rare cases of allergy to silicone materials may lead to itching or rash
- Temporary pore congestion – in heavy formulations the film may trap debris leading to small breakouts on acne prone skin
- Buildup on hair strands – repeated use in hair products can leave a coating that feels heavy or dull until shampooed out
- Reduced penetration of actives – the protective film might slow how quickly some water based ingredients reach the skin
If any discomfort, rash or other unwanted reaction develops stop use immediately and consult a healthcare professional.
Comedogenic Rating
Rating: 1 / 5
C30-45 Alkyldimethylsilyl Polypropylsilsesquioxane sits at the low end of the scale because its large silicone structure stays on the surface, allowing moisture to pass while keeping pore-clogging oils from building underneath. It also has a lightweight, non-greasy feel that does not create the heavy occlusive environment often linked to breakouts.
Most people who are prone to acne can use products containing this material without problems.
Keep in mind that the finished formula matters; if the ingredient is blended with thick butters or waxes the overall product could still trigger congestion even though this silicone alone is unlikely to do so.
Summary
C30-45 Alkyldimethylsilyl Polypropylsilsesquioxane is primarily a film former that lays down a flexible, breathable layer on skin or hair. That film locks in hydration, helps pigments and UV filters stay put, improves water and smudge resistance and gives products a smooth glide.
While not as famous as dimethicone, it has carved out a solid niche in long-wear makeup, sunscreens, primers and lightweight hair serums where brands want staying power without a heavy feel.
Current studies and decades of use show it to be low risk for irritation or systemic absorption, making it safe for most users. As with any new cosmetic, patch test first to be sure it agrees with your individual skin.