What Is Polyurethane-33?
Polyurethane-33 is a synthetic polymer created by first reacting dimethylolpropionic acid with a specialty polyester made from adipic acid, hexylene glycol and neopentyl glycol. This mixture is then combined with methylene dicyclohexyldiisocyanate (often shortened to SMDI) to form a prepolymer. Afterward the prepolymer is neutralized with triethylamine, then extended with hydrazine, producing a stable water-dispersible polyurethane. The result is a flexible film-forming material that can be blended easily into water-based cosmetic formulas.
Polyurethanes began appearing in consumer goods during the mid-20th century for coatings and foams. As cosmetic chemists searched for lightweight, long-lasting film formers in the 1990s, certain polyurethane chemistries like Polyurethane-33 were adapted for personal care. Their ability to create thin, invisible films without a tacky feel made them attractive for color cosmetics and hair styling products.
Today Polyurethane-33 shows up most often in mascaras, liquid eyeliners, long-wear foundations, transfer-resistant lip color, brow gels and some hair gels or edge tamers. Its compatibility with water means formulators can build long-wear claims while still offering easy wash-off and a comfortable feel.
Polyurethane-33’s Cosmetic Benefits/Uses
In personal care formulas Polyurethane-33 serves a single, but very valuable, purpose.
Binding: It acts as a film former that binds pigments, powders and other ingredients together, helping the final product adhere evenly to skin or hair. This improves wear time, reduces flaking or smudging in eye and lip products and allows hair gels to hold style with flexible, non-crunchy control.
Who Can Use Polyurethane-33
Polyurethane-33 is generally appropriate for all skin types. Its lightweight film does not create an occlusive barrier so oily and combination skins appreciate the non-greasy feel while dry skin can layer it over richer moisturizers without added heaviness. Highly sensitive skin may wish to monitor for redness because even low levels of residual monomers in the finished polymer could trigger irritation in a small percentage of users.
The ingredient is synthetic and contains no animal-derived matter, making it suitable for vegans and vegetarians provided the finished product is certified cruelty-free by the brand.
Current data show no special concerns for topical use during pregnancy or while breastfeeding, as the polymer is too large to penetrate beyond the uppermost skin layers. This is not medical advice and anyone who is pregnant or nursing should review all personal care choices with a healthcare professional.
Polyurethane-33 is not known to increase photosensitivity, so normal daytime sun protection practices are sufficient. It is also fragrance-free and free of common sensitizers, making it a low-risk option for most users.
Potential Side Effects/Adverse Reactions
Reactions to Polyurethane-33 vary from person to person. The issues listed below are possible yet uncommon when the ingredient is used at the low levels found in finished cosmetics.
- Mild redness, itching or stinging on very sensitive skin
- Allergic contact dermatitis triggered by trace residual isocyanates or hydrazine used during manufacturing
- Temporary eye watering or burning if product migrates into the eyes
- Rare clogged pores in individuals highly prone to comedones when used in multiple layers with other films or heavy makeup
If any irritation, rash or discomfort develops stop using the product and consult a healthcare professional if symptoms persist.
Comedogenic Rating
Rating: 1 / 5
Polyurethane-33 forms a thin breathable film that sits on top of the skin rather than seeping into pores, so it is unlikely to trap oil or dead cells the way heavier waxes or oils can. A rating of 1 reflects this low but not zero potential because very acne-prone users could experience congestion if they layer several film-forming products or do not remove makeup thoroughly at night.
In most cases the ingredient is considered suitable for people susceptible to breakouts, particularly when used in lightweight mascara, eyeliner or brow products.
Its water-dispersible nature also means it rinses away more easily than many long-wear polymers, further lowering the chance of pore blockage.
Summary
Polyurethane-33 is mainly valued as a binder and film former that locks pigments and styling agents in place for longer wear without a stiff or sticky feel. By creating a flexible micro-film it helps mascara resist smudging, keeps foundation from transferring and gives hair gels soft hold.
While not as famous as silicones or acrylates, it has carved out a steady niche in long-wear color cosmetics and certain hair stylers where water resistance and comfort are key selling points.
Current research and widespread industry use show Polyurethane-33 is generally safe for topical application with a very low risk of irritation or pore clogging. As with any new cosmetic, it is wise to do a quick patch test when trying products that contain it to confirm personal compatibility.