What Is Polyurethane-42?
Polyurethane-42 is a synthetic copolymer created by linking together three building blocks: Di-C12-13 Alkyl Tartrate, Hydrogenated Dilinoleyl Alcohol and isophorone diisocyanate. The result is a flexible film-forming material that behaves like a lightweight plastic. Polyurethanes have been part of everyday items since the 1940s but formulators began exploring specialized versions such as Polyurethane-42 for cosmetics in the late 1990s when consumers started favoring long-wear makeup and lightweight textures. To produce it, chemists react the fatty alcohol components with isophorone diisocyanate under controlled heat then neutralize and purify the mixture, yielding a stable polymer dispersed in water or solvent that is easy to blend into creams, gels or sprays.
Because of its film-forming talent, Polyurethane-42 shows up in products that need staying power or a smooth finish. You will commonly spot it in liquid foundations, mascaras, eyeliners, long-wear lip colors, primers, setting sprays and certain hair styling serums. Some sheet masks and overnight treatments also use small amounts to lock active ingredients onto the skin.
Polyurethane-42’s Cosmetic Benefits/Uses
In formulas Polyurethane-42 serves a single yet valuable purpose.
As a film former it creates a thin flexible layer on skin or hair that helps pigments adhere, boosts water and sweat resistance, reduces flaking and improves overall wear time. The film can also give products a smoother glide during application and leave a soft touch finish once dry.
Who Can Use Polyurethane-42
Polyurethane-42 is generally considered suitable for all skin types including dry, normal, combination and oily. Its lightweight flexible film rarely feels heavy or greasy so it does not typically clog pores or worsen shine. Sensitive skin can also tolerate it because the polymer is inert and does not penetrate deeply, though very reactive skin may still prefer fragrance-free formulas to limit overall irritation triggers.
The ingredient is synthetic and made without animal-derived materials so it is acceptable for vegans and vegetarians.
Current safety assessments have not shown any specific risks for people who are pregnant or breastfeeding when Polyurethane-42 is used topically at the levels found in cosmetics. This is not medical advice and anyone who is pregnant or nursing should consult a healthcare professional before adding new products, just to be safe.
Polyurethane-42 does not increase photosensitivity and will not make skin more prone to sunburn. It can actually help keep sunscreen pigments in place when used in sun care formulas.
Potential Side Effects/Adverse Reactions
Responses to topical Polyurethane-42 vary from person to person. The issues below are only potential effects and are unlikely for most users when the ingredient is used correctly in a well-formulated product.
- Mild skin irritation
- Redness or itching in people already prone to contact dermatitis
- Eye stinging if the product accidentally enters the eye area before it sets
- Build-up on hair shafts leading to dullness if heavy styling products are not washed out regularly
If any discomfort or visible reaction occurs discontinue use and seek guidance from a healthcare professional.
Comedogenic Rating
Rating: 1 / 5
Polyurethane-42 carries very little risk of clogging pores because it is a large inert polymer that sits on the surface rather than sinking into follicles. It does not add extra oil yet its film can create a light barrier, which is why it earns a cautious 1 instead of a perfect 0. Overall it is considered safe for acne-prone skin and rarely triggers breakouts.
Because the polymer is removed with normal cleansing and is used at low percentages, significant pore build-up is unlikely unless heavy layers are left on for multiple days.
Summary
Polyurethane-42 is a synthetic film former that locks pigments in place, increases water and sweat resistance, smooths application and helps finished makeup feel flexible rather than stiff. It achieves these effects by forming an ultra-thin mesh over skin or hair that bonds to the product underneath while remaining breathable.
The ingredient is popular in long-wear foundations, waterproof mascaras and setting sprays but you will not find it in every cosmetic aisle staple, so its presence is notable but not ubiquitous.
Current data shows Polyurethane-42 is low risk for irritation, non-sensitizing and appropriate for all skin types including sensitive. As with any new skincare or makeup ingredient it is smart to patch test a product first to confirm personal tolerance and peace of mind.