Ingredient review

Steareth-100

INCI: STEARETH-100

Steareth-100 is a gentle synthetic emulsifier that helps blend oil and water in creams and cleansers, with a low risk of irritation.

beautyskincareemulsifier

In plain English

Steareth-100 is a man-made ingredient that helps oil and water mix together in your skincare products. It's a type of emulsifier, meaning it keeps the formula from separating into layers. Think of it like a friendly bridge between water-loving and oil-loving ingredients, making your lotion or cleanser smooth and stable. It's made from stearyl alcohol (a fatty alcohol from plants or petroleum) that's been reacted with ethylene oxide to make it water-friendly. Because it's a large molecule, it stays mostly on the skin's surface and is unlikely to cause irritation or clog pores.

Review score

Safety, usefulness, and evidence

3.8Good
3.8/ 5

Potentially useful with some tradeoffs

The evidence base is useful, but some claims depend heavily on the formula.

Risk flags are low for most users, though the finished product can still irritate.

Source
synthetic
Evidence
moderate
Irritation
low
Clogging risk
low
How reviews are scored

Quick decision guide

Useful, but context matters

Steareth-100 is generally a lower-concern ingredient when the full formula suits your skin.

Plain-English read

Treat this as a practical screening step before you compare products that contain this ingredient.

  1. Step 1Start with the score, then check the irritation and clogging risk before judging Steareth-100.
  2. Step 2Use the "Best for" and "Use caution if" sections to match the ingredient to your skin, not just to a marketing claim.
  3. Step 3If a product stings, breaks you out, or worsens irritation, judge the finished formula and stop using it even if the ingredient scores well.

Score terms in plain English

Irritation risk

low

Less likely to sting, burn, or bother most users, though sensitive skin can still react.

Clogging risk

low

Less likely to feel heavy or contribute to clogged pores for most skin types.

Evidence level

moderate

There is useful support, but formula details and claim strength still matter.

What it is

Steareth-100 is a synthetic emulsifier derived from stearyl alcohol and ethylene oxide. The number '100' indicates the average number of ethylene oxide units, making it a high-ethoxylate surfactant that is very water-soluble and mild.

How it works

In a cosmetic product, Steareth-100 positions itself at the boundary between oil and water droplets. Its water-loving (hydrophilic) end dissolves in water, while its oil-loving (lipophilic) tail embeds in oil. This stabilizes the mixture, preventing separation and giving the product a uniform, creamy texture. It also helps cleanse by reducing surface tension, allowing dirt and oil to be rinsed away.

Pros

Gentle emulsifier

Steareth-100 is considered very mild and is unlikely to cause stinging or irritation, even for sensitive skin, because its large molecule stays on the surface.

Improves product feel

It helps create a smooth, non-greasy texture in creams and lotions, making them easier to apply and more pleasant to use.

Cons and cautions

Potential trace impurities

During manufacturing, ethylene oxide can form 1,4-dioxane, a possible carcinogen. However, reputable brands purify their ingredients to keep levels extremely low and safe.

Not natural

Steareth-100 is fully synthetic, which may be a drawback for consumers seeking plant-based or naturally derived skincare.

Best for

  • People with normal to dry skin looking for stable, non-irritating moisturizers
  • Those who prefer synthetic emulsifiers over natural alternatives for consistency

Use caution if

  • Individuals with known sensitivity to ethoxylated ingredients or a history of reactions to 1,4-dioxane (rare)

Usage tips

Use products containing Steareth-100 as directed; it works best in formulations with both water and oil phases.
If you have very sensitive skin, patch test a new product on your inner arm before full use.

Safety summary

Steareth-100 is considered safe for use in cosmetics at typical concentrations. The main safety concern is potential contamination with 1,4-dioxane, but regulatory limits and purification methods keep levels negligible. It has low irritation and comedogenic potential.

Research notes

The Cosmetic Ingredient Review (CIR) has evaluated Steareth-100 and similar ethoxylated alcohols, concluding they are safe in current usage patterns. No significant human or animal studies indicate toxicity at cosmetic levels. Evidence is based on structural similarity and industry safety data.

Common label clues

Typical concentration
Usually 0.5–5% in rinse-off products; lower in leave-on formulas
Regulatory status
Approved for use in cosmetics in the US (FDA), EU (CosIng), and many other countries. The Cosmetic Ingredient Review (CIR) panel has deemed it safe as used in cosmetics, with restrictions on 1,4-dioxane levels.
Common uses
Moisturizers, Cleansers, Creams, Lotions
Environmental note
Steareth-100 is synthetic and not readily biodegradable. Its production involves ethylene oxide, which is derived from fossil fuels. Environmental impact is moderate compared to natural alternatives.

Good to know

  • The '100' in Steareth-100 refers to the number of ethylene oxide units, which makes it more water-soluble and milder than lower-numbered Steareths.
  • It is often used alongside other emulsifiers to fine-tune texture and stability.

Common questions

What is Steareth-100 in beauty products?

Steareth-100 is a man-made ingredient that helps oil and water mix together in your skincare products. It's a type of emulsifier, meaning it keeps the formula from separating into layers. Think of it like a friendly bridge between water-loving and oil-loving ingredients, making your lotion or cleanser smooth and stable. It's made from stearyl alcohol (a fatty alcohol from plants or petroleum) that's been reacted with ethylene oxide to make it water-friendly. Because it's a large molecule, it stays mostly on the skin's surface and is unlikely to cause irritation or clog pores.

What does Steareth-100 do in a beauty product?

In a cosmetic product, Steareth-100 positions itself at the boundary between oil and water droplets. Its water-loving (hydrophilic) end dissolves in water, while its oil-loving (lipophilic) tail embeds in oil. This stabilizes the mixture, preventing separation and giving the product a uniform, creamy texture. It also helps cleanse by reducing surface tension, allowing dirt and oil to be rinsed away.

Is Steareth-100 safe for most people?

Steareth-100 is considered safe for use in cosmetics at typical concentrations. The main safety concern is potential contamination with 1,4-dioxane, but regulatory limits and purification methods keep levels negligible. It has low irritation and comedogenic potential.

Who should be careful with Steareth-100?

Individuals with known sensitivity to ethoxylated ingredients or a history of reactions to 1,4-dioxane (rare)

Research sources

Cosmetic Ingredient Review (CIR) – Safety Assessment of Steareth-100OpenFDA – Cosmetics Ingredients DatabaseOpenEuropean Commission CosIng DatabaseOpen

Ingredient reviews are educational and are not medical advice. Patch test new products and ask a licensed clinician about persistent irritation, allergies, pregnancy-specific questions, or diagnosed skin conditions.