What Is Peg-9?
Peg-9 is the shorthand name for poly(oxy-1,2-ethanediyl), α-hydro-ω-hydroxy-, with an average of nine ethylene oxide units linked together. In simple terms it is a lightweight form of polyethylene glycol created by reacting ethylene oxide with water or ethylene glycol under heat and pressure. The result is a clear, nearly odorless liquid that mixes well with both water and oils.
Polyethylene glycols have been part of personal care formulas since the 1950s when chemists discovered their ability to pull in moisture and dissolve many ingredients that would otherwise separate. Peg-9 sits at the lower end of the PEG size scale so it spreads easily on skin without leaving a heavy film.
You will spot Peg-9 in a wide range of products such as facial moisturizers, hydrating masks, essence-style serums, lightweight lotions, after-sun gels, makeup removers, hair conditioners and even some deodorant sticks. Formulators like it because it plays well with active ingredients, helps stabilize emulsions and gives products a smooth non-sticky feel.
Peg-9’s Cosmetic Benefits/Uses
Below are the key roles Peg-9 plays when added to a topical formula.
- Humectant – attracts water from the environment and from deeper layers of skin to the surface, helping keep skin feeling soft and supple and reducing the look of fine lines caused by temporary dryness
- Solvent – dissolves and evenly disperses other ingredients such as botanical extracts, fragrances or preservatives so the finished product stays uniform and performs the same with every use
Who Can Use Peg-9
Peg-9 is generally gentle enough for most skin types. Dry and normal skin benefit from its water-binding talent while oily and combination skin appreciate its light feel that does not leave a greasy film. Sensitive skin usually tolerates it as well, though anyone with a known allergy to polyethylene glycols or with a severely damaged skin barrier may prefer to steer clear until a dermatologist gives the green light.
Because Peg-9 is made from petroleum-derived raw materials and does not rely on animal sources it is suitable for both vegetarians and vegans.
Peg-9 has a long record of safe use in products marketed to pregnant and breastfeeding women. Current safety reviews have found no evidence that it poses a risk at the low levels used in cosmetics. Nonetheless this is not medical advice and anyone who is pregnant or nursing should run any skincare product past a qualified health professional just to be safe.
The ingredient does not make skin more sensitive to sunlight so it does not raise the risk of sunburn. It also plays nicely with most other common skincare actives and preservatives.
Potential Side Effects/Adverse Reactions
Side effects from topical Peg-9 vary from person to person. The issues listed below are only potential outcomes and are not what the average user should expect. When the ingredient is used at the concentrations allowed in cosmetics most people experience no problems.
- Mild skin irritation some people may notice temporary redness or itching especially on compromised or freshly exfoliated skin
- Contact allergy a small number of users can develop an allergic reaction to polyethylene glycols leading to rash swelling or hives
- Eye stinging if a formula containing Peg-9 gets into the eyes it can cause brief discomfort or watering
- Enhanced penetration of other ingredients Peg-9 can help other substances absorb more deeply which in rare cases may increase the chance of irritation from those substances
- Impurity concerns trace levels of manufacturing by-products such as 1,4-dioxane may be present though reputable brands keep these within strict safety limits
If you experience any unwanted reaction stop using the product and seek advice from a healthcare professional
Comedogenic Rating
Rating: 0/5
Peg-9 is fully water soluble and leaves almost no residue on the skin so it does not create the kind of greasy film that can trap dead cells or sebum inside pores. Studies and decades of cosmetic use show no link between Peg-9 and the formation of comedones, which is why it earns a zero on the clog-pore scale.
This means Peg-9 is generally suitable for people who are prone to acne or breakouts.
Because it rinses cleanly, Peg-9 can actually help reduce the need for heavier emulsifiers in a formula, indirectly supporting a clearer complexion.
Summary
Peg-9 works as a humectant and solvent. Its small polyethylene glycol chain draws moisture to the skin’s surface, adding a quick hit of hydration, while its excellent dissolving power keeps oils, fragrances and actives evenly dispersed for a smoother, more stable product.
It is a quiet performer rather than a headline ingredient but its versatility has kept it in moisturizers, cleansers, hair conditioners and after-sun gels since the mid-twentieth century.
Safety evaluations place Peg-9 in the low-risk category for topical use. Most skin types tolerate it well and adverse reactions are rare. As with any new product it is wise to patch test first to make sure your individual skin is on board.