Steareths are essentially polyethylene glycol (PEG) ethers of stearic acid, i.e. they’re formulated by reacting stearyl alcohol with ethylene oxide to form polyoxyethylene stearyl ethers. Ethylene oxide is a proven cancer-causing chemical (carcinogen) whose effects have been discussed elsewhere here (see PEG, phenoxyethanol sodium laureth sulfate, ammonium laureth sulfate, and polysorbates).
Steareths come in various series, e.g. steareths -2, -4, -6, -7, -10, -11, -13, -15, and -20. Each numerical value provides an indication of the average number of ethylene oxide used in formulating that steareth. Steareth-15, for example, is prepared by ethoxylating stearyl alcohol with 15 units of ethylene oxide.
Steareths are used in personal care products as surfactants, emulsifiers, wetting agents, and coupling agents. They are also used as solubilizers to minimize the chances of certain ingredients separating into individual components, e.g. water and oil.
All products containing such ethoxylated ingredients should be avoided as much as possible. This is because ethoxylation can produce 1,4-dioxane, which has been classified as carcinogenic by the International Center for Research on Cancer and the US Environment Protection Agency (see ammonium laureth sulfate, polysorbates, sodium laureth sulfate, and PEG for more information on ethoxylation and 1,4-dioxane).
There’re three possible ways to ascertain if a product has an ethoxylated ingredient. Firstly, look for the term polyethylene glycol or the prefix ‘PEG.’ Second, search to see if there’s any ‘eth’ suffix listed, e.g. ceteareth-25. Lastly, see if any of the ingredients contains dashes followed immediately by a number e.g. steareth-21.
Some manufacturers of mainstream and natural personal care products include steareths in their formulations, arguing that steareths-2 to -20 can be safely used so long as the concentration is below 25%. The real issue, however, is that it’s difficult to ascertain the quantity of steareth that’s been used in your product formulation unless this is stated, which is quite rare.
In addition to its carcinogenic properties, steareths can cause skin irritations and reproductive problems, including low motile sperm count. They can also cause developmental problems and impairment of the endocrine system.