What Is Oleth-100?
Oleth-100 is a synthetic ingredient created by reacting oleyl alcohol, a fatty alcohol often derived from plant oils like olive or beef tallow, with ethylene oxide. This reaction attaches approximately one hundred ethylene oxide units to the oleyl alcohol backbone, turning the oil-like molecule into a water-soluble surfactant. The process, called ethoxylation, has been used in the cosmetics industry since the mid 20th century to make oil-derived materials compatible with water-based formulas.
Its ability to bridge oil and water quickly caught the attention of formulators who needed reliable cleansing agents that would not leave heavy residue. Over time Oleth-100 has appeared in a wide range of rinse-off and leave-on products, particularly where a mild yet effective cleanser is required. You are most likely to find it in shampoos, body washes, facial cleansers, makeup removers, micellar waters and certain exfoliating masks. Because it behaves well alongside many other ingredients, it can also show up in specialty items such as pre-shave oils and gentle baby washes.
Oleth-100’s Cosmetic Benefits/Uses
Oleth-100 serves one primary role in personal care formulas.
Cleansing: As a non-ionic surfactant, Oleth-100 lifts dirt, excess oil and product buildup from skin or hair so they can be rinsed away with water. Its high ethoxylation level gives it excellent solubility and low irritation potential, allowing formulators to create cleansers that feel mild yet still leave the surface fresh and free of residue.
Who Can Use Oleth-100
Oleth-100 is generally well tolerated by most skin types, including normal, oily, combination and dry. Sensitive skin can usually handle it too because the ingredient is non ionic and therefore tends to be less irritating than many anionic cleansers. People with very reactive or highly compromised skin should still watch for any personal triggers as even mild surfactants can feel drying if overused.
For those following vegan or vegetarian lifestyles, Oleth-100 is considered suitable when the starting oleyl alcohol comes from plant oils like olive or sunflower. Some manufacturers may source it from animal fat so anyone avoiding animal-derived materials should check the product label or reach out to the brand for confirmation.
Current safety data does not flag Oleth-100 as a concern for women who are pregnant or breastfeeding. Even so this is not medical advice and anyone who is expecting or nursing should show the full ingredient list of any product to their healthcare provider before use, just to be safe.
The ingredient does not increase photosensitivity, so there is no need for extra sun precautions beyond your usual daily SPF routine. It also works well across different hair types and textures, making it a flexible choice in shampoos and cleansing conditioners.
Potential Side Effects/Adverse Reactions
Reactions to topical Oleth-100 vary from person to person. The effects listed below are only potential outcomes and most users will not experience them when the ingredient is properly formulated in a product.
- Mild skin dryness – extended contact time or high concentrations can strip natural oils
- Transient redness or stinging – more likely on very sensitive or damaged skin barriers
- Eye irritation – if a cleanser accidentally gets into the eyes it may cause temporary discomfort
- Allergic contact dermatitis – rare but possible for individuals with a specific sensitivity to ethoxylated surfactants
If you experience any of the above reactions stop using the product and consult a healthcare professional for guidance.
Comedogenic Rating
Rating: 1/5
Oleth-100 is highly water soluble and designed to rinse away cleanly so it rarely lingers in pores long enough to clog them. Its large ethoxylated structure also keeps it from packing tightly inside follicles, further lowering the risk of comedones. Because of this it is generally acceptable for acne-prone or breakout-prone skin, especially in rinse-off formats. The main thing to watch is the overall formula: heavy oils or waxes paired with Oleth-100 could still create congestion even though the surfactant itself is low risk.
Summary
Oleth-100 is a synthetic surfactant that lifts oil, dirt and product residue so they can be washed away with water. By attaching about one hundred ethylene oxide units to oleyl alcohol, chemists turned a fatty alcohol into a gentle cleanser that blends smoothly into both water-based and oil-based systems.
It is a solid workhorse in shampoos, facial cleansers, micellar waters and even some leave-on products, though it is not a headline ingredient that marketers spotlight. Its popularity sits in the middle of the pack: common enough that formulators trust it yet not so trendy that consumers talk about it by name.
Current data shows Oleth-100 is safe for most skin types with a very low chance of irritation or pore clogging when used as directed. As with any new cosmetic ingredient it is smart to patch test a product before full use to make sure your skin agrees with the complete formula.