What it is
The EU's CosIng database gives its chemical name as hexadecan-1-ol, a chain of 16 carbon atoms, and its European Pharmacopoeia name as alcohol cetylicus.1 It belongs to the same family as Stearyl Alcohol, with 18 carbon atoms2, and the mixture of the two is listed as Cetearyl Alcohol.3
What it does in a formula
CosIng lists eight functions: emollient, emulsifying, emulsion stabilising, foam boosting, fragrance, opacifying, cleansing and viscosity controlling.1 In a cream that mostly means softening the skin's surface, helping oil and water stay mixed, making the product opaque and setting its thickness.
The thickening is partly a matter of structure. In a study of oil-in-water creams, the cream's semisolid body came from a gel network that cetyl alcohol formed with a non-ionic surfactant and water. When a cationic polymer was added, the cream lost much of its structure, and the data suggested the network had turned into crystals of cetyl alcohol.4 The same ingredient can behave differently depending on what else is in the formula.
A fatty alcohol, not ethanol
The US FDA explains that in cosmetic labelling "alcohol" on its own means ethyl alcohol, and that products labelled "alcohol free" may contain fatty alcohols such as cetyl alcohol, whose effects on the skin are quite different from those of ethyl alcohol.5 Ethanol appears on a label as Alcohol6 or Alcohol Denat..5
What sources say
Allergic reactions to fatty alcohols have been described in case reports. In one, two people developed allergic contact dermatitis from an ointment, traced to its cetearyl alcohol, the cetyl and stearyl mixture.7 Case reports show that a reaction is possible, not how common it is. If you have had a confirmed reaction to cetyl alcohol, look for Cetearyl Alcohol on the list as well, because that mixture contains it.3 The list will not tell you how much is present.
How it appears on a label
As Cetyl Alcohol. If a list says Cetearyl Alcohol instead, that is the cetyl and stearyl mixture; Ceteareth followed by a number is a different ingredient, a PEG ether made from cetearyl alcohol.8 The ingredient checker shows which is which on a list you paste in.