What Is Bis-Hydroxypropyl Dimethicone/Smdi Copolymer?
Bis-Hydroxypropyl Dimethicone/SMDI Copolymer is a silicone-based ingredient created by linking bis-hydroxypropyl dimethicone with small units of saturated bis-methylene diisocyanate. The result is a flexible branched polymer that behaves like a lightweight silicone film on the skin or hair. Silicones have been staples in cosmetics since the 1950s thanks to their silky feel and water-resistant properties. This newer copolymer was introduced in the early 2000s when formulators wanted a more breathable alternative to heavier silicones used in long-wear makeup and humidity-proof hair care.
The manufacturing process starts with medical-grade silica that is transformed into basic silicone oils. These oils are then reacted with propylene oxide to add the hydroxypropyl groups. Finally, controlled amounts of SMDI are added to crosslink the chains, forming a stable network that does not break down easily in water or under heat. All steps are done in closed reactors to keep the material free from contaminants and to comply with cosmetic safety standards.
You will most often spot Bis-Hydroxypropyl Dimethicone/SMDI Copolymer in long-lasting foundations, transfer-resistant lipsticks, waterproof mascaras, leave-in hair serums, anti-frizz sprays, sheet masks and overnight moisturizers. Its ability to form a thin but durable film makes it ideal wherever brands promise extended wear or protection against humidity.
Bis-Hydroxypropyl Dimethicone/Smdi Copolymer’s Cosmetic Benefits/Uses
This ingredient pulls double duty in formulations, offering both sensory and performance benefits
- Film Forming: Creates an invisible flexible layer that locks pigments in place, boosts water resistance and helps active ingredients stay on the skin or hair longer
- Emollient: Adds a smooth glide during application, softens rough patches and leaves a conditioned finish without feeling greasy
Who Can Use Bis-Hydroxypropyl Dimethicone/Smdi Copolymer
Thanks to its lightweight film and low occlusion potential this silicone copolymer suits nearly every skin type including dry, normal, combination and oily skin. Sensitive complexions generally tolerate it well because the polymer is inert and fragrance free. Those with very acne prone skin may want to monitor how their pores respond, as layering any film former over comedogenic ingredients can trap debris and worsen breakouts.
Bis-Hydroxypropyl Dimethicone/SMDI Copolymer is fully synthetic and contains no animal derived raw materials so it aligns with vegan and vegetarian preferences. Cruelty free status depends on the finished brand’s testing policies not the ingredient itself.
The molecule is large, does not penetrate deeply and is not known to interfere with hormones which means it is considered low risk for pregnant or breastfeeding women. This is not medical advice and anyone who is pregnant or nursing should confirm every skincare choice with a physician to be safe.
The ingredient does not cause photosensitivity and will not make skin more prone to sunburn. It also has no known interactions with common actives like retinol, vitamin C or acids, making it easy to slot into most routines.
Potential Side Effects/Adverse Reactions
Reactions to topical Bis-Hydroxypropyl Dimethicone/SMDI Copolymer vary from person to person. The following are potential side effects and are unlikely to be the typical user experience when the ingredient is used correctly in a cosmetic formula.
- Transient skin irritation such as mild redness or itching in individuals sensitive to silicones
- Stinging or watering if the product accidentally gets into the eyes
- Build up on hair leading to a heavy or limp feel when used in multiple styling layers without proper cleansing
- Acne flare ups in users whose skin reacts negatively to any occlusive film when combined with other pore clogging substances
If you experience any unwanted reaction stop using the product and seek advice from a medical professional or dermatologist.
Comedogenic Rating
Rating: 1 out of 5
Bis-Hydroxypropyl Dimethicone/SMDI Copolymer earns a low score because its large branched structure sits on top of the skin rather than seeping into pores and it is not oily or waxy. While it forms a film the layer is thin and breathable so it is unlikely to clog follicles on its own. This makes the ingredient generally suitable for people prone to acne or breakouts, though results can vary depending on the full product formula and how thoroughly it is removed.
Most reports of congestion involve heavy layering with other rich ingredients or inadequate cleansing, not the copolymer itself. Using a gentle but effective cleanser will help keep buildup from becoming an issue.
Summary
Bis-Hydroxypropyl Dimethicone/SMDI Copolymer acts as a film former and emollient, laying down a lightweight flexible shield that locks makeup pigment in place, boosts water resistance and leaves skin or hair feeling silky. Its branched silicone backbone provides slip while the crosslinked network stays put during heat or humidity, which is why formulators choose it for long wear cosmetics and anti frizz hair products.
The ingredient has carved out a niche in transfer resistant foundations waterproof mascaras and smoothing serums, though it is not as ubiquitous as classic dimethicone. Brands looking for a lighter breathable silicone often turn to this copolymer.
Safety data show a very low risk of irritation or systemic absorption and it is considered pregnancy safe vegan friendly and non photosensitizing. As with any new product a small patch test is a smart step to confirm personal tolerance before full use.