What Is Peg-9 Stearamide Carboxylic Acid?
Peg-9 Stearamide Carboxylic Acid is a man-made ingredient created by linking stearic acid, a fatty acid usually sourced from vegetable oils, with roughly nine units of ethylene oxide. This link forms a mild surfactant that loves both oil and water, making it ideal for blending the two. Chemists first began testing this type of molecule in the 1970s when the demand for smoother cream textures grew and safer alternatives to harsh detergents were needed. Today the ingredient is produced in large batches through a controlled reaction that attaches the ethylene oxide units to stearic acid, followed by a carboxylation step that boosts its water-friendly side. The finished material is a soft, wax-like solid that disperses easily when heated.
You will most often see Peg-9 Stearamide Carboxylic Acid in face creams, body lotions, sunscreens, liquid foundations, rinse-off masks and gentle cleansers. Brands use it when they want a stable product that feels rich but not greasy, stays mixed on the shelf and spreads evenly on the skin.
Peg-9 Stearamide Carboxylic Acid’s Cosmetic Benefits/Uses
This ingredient serves mainly as an emulsifier. By sitting at the boundary between oil and water, it holds the two phases together so the formula stays smooth and uniform. A good emulsion not only looks better but also delivers active ingredients more evenly, reduces the risk of separation during storage and gives creams a silky glide that users enjoy.
Who Can Use Peg-9 Stearamide Carboxylic Acid
This emulsifier is gentle enough for most skin types, including normal, dry, combination and sensitive skin. Its fatty acid base can add a touch of richness, which dry or mature complexions often appreciate. People with very oily or acne-prone skin can usually still tolerate it, but those who find that richer creams clog their pores may prefer lighter formulas.
The stearic acid used to make Peg-9 Stearamide Carboxylic Acid is frequently sourced from plants such as coconut or palm, making many finished materials suitable for vegetarians and vegans. Some suppliers still use animal-derived stearic acid, so strict plant-based users should look for a clear vegan label or confirmation from the brand.
No specific warnings exist for women who are pregnant or breastfeeding. Current safety data show low systemic absorption and no known fetal or lactation risks. This is not medical advice, and anyone who is expecting or nursing should run new skincare products past a doctor just to be safe.
Peg-9 Stearamide Carboxylic Acid does not cause photosensitivity, so it will not make skin more prone to sunburn. It is also considered eye-area safe at the levels normally used in creams and cleansers.
Potential Side Effects/Adverse Reactions
Side effects from topical Peg-9 Stearamide Carboxylic Acid can vary from person to person. The list below covers possible reactions, but they are uncommon when the ingredient is used correctly in a well-formulated product.
- Mild skin irritation – a rare tingling or redness, usually short-lived
- Contact dermatitis – an allergic rash in individuals sensitive to polyethylene glycols or stearic acid derivatives
- Eye stinging – possible if a high-concentration product gets into the eyes before rinsing
- Acne flare-up – uncommon, but can happen in those already prone to clogged pores when the formula is rich in other oils or waxes
If any of these reactions occur, stop using the product and consult a healthcare professional.
Comedogenic Rating
Rating: 1 / 5
Peg-9 Stearamide Carboxylic Acid scores low because the polyethylene glycol side makes it highly water friendly, which helps it rinse or wear off without lingering in pores. While the stearic acid portion is a fatty component with a mild tendency to clog, the attached PEG chain keeps the molecule mobile and less likely to form a waxy film.
Most people who are prone to acne can use products containing this ingredient without seeing new breakouts, as long as the overall formula is lightweight.
If the product is packed with other heavy oils or butters, the combined load could still feel occlusive on very oily skin, so texture and full ingredient list matter.
Summary
Peg-9 Stearamide Carboxylic Acid is mainly an emulsifier that binds water and oil so creams stay smooth, active ingredients distribute evenly and the finished texture feels silky. It does this by positioning its water loving PEG chain in the aqueous phase while its fatty stearic tail anchors into the oil phase, locking the two together.
The ingredient is moderately popular in mainstream skincare and makeup. It is not as common as basic emulsifiers like glyceryl stearate but formulators reach for it when they need extra stability in richer creams or sunscreen blends.
Current research and decades of safe cosmetic use show low irritation potential and minimal risk of systemic absorption. As with any new skincare product, patch test first to be on the safe side.