What Is Pei-700?
Pei-700 is the cosmetic trade name for an aziridine homopolymer, a man-made chain of small ring-shaped molecules called aziridines. Unlike plant oils or mineral clays, this ingredient is entirely synthetic and created in a controlled laboratory setting. The process starts with the simple aziridine monomer, which is opened and linked repeatedly in the presence of catalysts to form a water-soluble polymer with flexible, nitrogen-rich backbones. Chemists can tailor the length of these chains to hit a target average molecular weight of roughly 700, which is where the “700” in the name comes from.
Polymers like Pei-700 first caught formulators’ attention in the late 20th century as the beauty industry looked for alternatives to traditional thickeners that could work well in both water-based and hybrid formulas. Thanks to its reliable performance across a range of pH levels and temperatures, it soon found a place in modern skin and hair care labs.
Today you are most likely to spot Pei-700 on the ingredient list of sheet masks, rinse-off masks, lightweight gel moisturizers, serums, hair conditioners and styling creams. In each of these products it helps the formula keep a pleasant, easy-to-spread texture that feels neither too runny nor too heavy.
Pei-700’s Cosmetic Benefits/Uses
Pei-700 plays one main role in beauty products, but it is an important one that can influence how enjoyable a formula feels on the skin or hair.
Viscosity controlling: By thickening the water phase and helping oil and water stay evenly mixed, Pei-700 allows formulators to fine-tune a product’s texture. This gives creams their cushiony feel, prevents serums from dripping down your hand, and ensures masks stay in place for the recommended wear time. Stable viscosity also helps keep active ingredients evenly dispersed so every application delivers the intended benefits.
Who Can Use Pei-700
Because it is water soluble and used at low concentrations, Pei-700 is generally considered suitable for most skin types including dry, oily, combination and normal skin. People with very sensitive or compromised skin may want to keep an eye on how their skin feels, as cationic polymers can occasionally trigger mild irritation in that group.
The ingredient is fully synthetic and contains no animal derived raw materials, making it appropriate for vegans and vegetarians.
No studies have shown specific risks for pregnant or breastfeeding women when Pei-700 is applied topically in a finished cosmetic. This is not medical advice and any expectant or nursing parent should run their skincare routine past a qualified healthcare professional before use, just to be safe.
Pei-700 does not make skin more reactive to sunlight and is not known to interfere with sunscreen performance. It also plays well with most other common cosmetic ingredients, so formulators can add it without worrying about unwanted chemical reactions.
Potential Side Effects/Adverse Reactions
Reactions to topical Pei-700 vary from person to person. The points below outline potential side effects but most users will not experience them when the ingredient is used correctly in a professionally formulated product.
- Mild skin irritation: a fleeting feeling of warmth, itching or redness can appear, especially on very sensitive skin
- Temporary stinging on application: more likely if the product is used on freshly exfoliated or broken skin
- Allergic contact dermatitis: rare but possible; presents as persistent redness, swelling or small bumps
- Eye irritation: may cause watering or stinging if the product accidentally gets into the eyes
- Build up on hair or scalp: overuse in leave-in hair products can leave strands feeling coated or heavy until the next wash
- Enhanced penetration of other actives: its polymer structure can occasionally increase the delivery of small molecules, which might intensify the effects of strong exfoliants or retinoids used in the same routine
If you notice any discomfort or unexpected reaction while using a product that contains Pei-700, stop using it and consult a healthcare professional.
Comedogenic Rating
Rating: 0 / 5
Pei-700 is a lightweight water-soluble polymer that sits on the surface in a thin film then rinses away easily, so it does not block pores or trap oil. It contains no fatty acids or waxy residues that typically cause comedones, which is why it earns a zero rating.
That makes Pei-700 generally suitable for those prone to acne or breakouts.
Because it can slightly enhance penetration of other actives, people using strong acne treatments may notice quicker uptake of those ingredients, but Pei-700 itself will not add to clogging potential.
Summary
Pei-700 is a lab-crafted aziridine homopolymer used mainly to control viscosity, giving lotions, serums and masks a smooth spreadable feel while helping water and oil stay evenly mixed. It achieves this by forming a flexible, nitrogen-rich network that thickens the water phase without heaviness.
The ingredient has a quiet presence in the market: not as famous as hyaluronic acid yet valued by formulators who need reliable texture control in lightweight products.
Safety data show low irritation and no comedogenicity at typical use levels, so most people can use products containing Pei-700 without concern. As with any new cosmetic ingredient, it is smart to do a quick patch test the first time you try it, just to be certain your skin agrees with it.