What Is Peg-45 Stearate Phosphate?
Peg-45 Stearate Phosphate is a synthetic ingredient created by linking stearic acid, a fatty acid commonly derived from vegetable oils, with an average of 45 units of ethylene oxide and then adding a phosphate group. The result is a water-loving yet oil-compatible molecule that behaves a bit like a soap but is far gentler on skin.
The idea of combining fatty acids with polyethylene glycol (PEG) chains first gained popularity in the 1950s when formulators were looking for milder alternatives to traditional soaps. Adding a phosphate group later improved the molecule’s stability and skin feel, which helped Peg-45 Stearate Phosphate find its way into modern personal care formulas during the 1990s.
Commercial production starts with stearic acid sourced from plant oils such as coconut or palm. The acid reacts with ethylene oxide in a controlled environment to attach approximately 45 repeating oxyethylene units. This intermediate is then treated with phosphoric acid to create the final phosphate ester. After purification the ingredient appears as an off-white paste or solid that disperses easily in water.
You will most often see Peg-45 Stearate Phosphate in facial cleansers, foaming masks, body washes, micellar waters and makeup removers where a mild yet effective cleansing agent is needed. It can also show up in exfoliating scrubs or men’s grooming products aimed at delivering a clean feel without stripping the skin.
Peg-45 Stearate Phosphate’s Cosmetic Benefits/Uses
This ingredient is included in formulas primarily for one key job:
Cleansing: Peg-45 Stearate Phosphate lowers the surface tension between oil, dirt and water so impurities lift away from skin with minimal effort. Because its fatty acid tail loves oil while its PEG-phosphate head loves water, it can grab onto greasy debris then rinse clean, leaving the skin feeling fresh but not tight.
Who Can Use Peg-45 Stearate Phosphate
Because it is a mild, water-dispersible cleanser, Peg-45 Stearate Phosphate suits most skin types including oily, combination, normal and even sensitive skin that cannot tolerate harsher surfactants. Extremely dry or eczema-prone skin might feel a little tight if the overall formula lacks added moisturizers, so those users should look for products that pair the ingredient with soothing oils or humectants.
The stearic acid portion of this molecule is usually sourced from plant oils which makes it suitable for vegans and vegetarians. If avoiding animal-derived ingredients is critical, check the brand’s sourcing statement to confirm the fatty acid is plant based.
Current safety data show no special restrictions for women who are pregnant or breastfeeding because systemic absorption is negligible. This is not medical advice, and anyone who is expecting or nursing should review any skincare product with a qualified healthcare provider just to be safe.
Peg-45 Stearate Phosphate does not increase photosensitivity, so there is no need to alter your normal sun protection habits when using products that include it.
Potential Side Effects/Adverse Reactions
Reactions to topical Peg-45 Stearate Phosphate vary from person to person. The points below list potential effects that could occur, though most users will not experience them when the ingredient is used correctly in a well-formulated product.
- Mild skin irritation – a temporary feeling of stinging or burning, most likely in people with very sensitive or compromised skin
- D dryness or tightness – possible if the rest of the formula lacks sufficient emollients, especially for users with pre-existing dryness
- Contact dermatitis – rare allergic response that can show up as redness, itching or small bumps
- Eye irritation – tearing or slight burning if the product accidentally gets into the eyes
If you notice any uncomfortable reaction discontinue use and consult a healthcare professional or dermatologist for guidance.
Comedogenic Rating
Rating: 1 out of 5 – Peg-45 Stearate Phosphate is highly water soluble thanks to its long PEG chain and phosphate group, so it rinses off the skin instead of lingering in pores. The small amount of fatty acid it contains is balanced by the cleansing head of the molecule, which keeps the overall residue level low. For most people, including those prone to clogged pores, this ingredient is considered very low risk for triggering breakouts. Only in very heavy or poorly formulated products could it possibly contribute to congestion.
Summary
Peg-45 Stearate Phosphate is used in skincare as a gentle cleanser that lifts oil, dirt and makeup without stripping the skin. It does this by combining an oil-loving stearic acid tail with a water-loving PEG-phosphate head, letting it grab greasy debris then wash away clean.
While not as famous as classic surfactants like sodium lauryl sulfate, it shows up steadily in modern face washes, micellar waters and other mild cleansing products where a softer feel is desired.
Current research and decades of use suggest it is safe for the vast majority of users with only rare reports of irritation. As with any new skincare ingredient it is smart to perform a quick patch test when trying a fresh product that contains Peg-45 Stearate Phosphate, just to be sure your skin agrees with it.