Stearic Acid.

What it does

It acts as an emollient, a thickener that gives body to creams, and a co-emulsifier that helps stabilize oil-and-water blends; it also saponifies into soap.

Benefits

• Thickens and gives body to creams, lotions, and balms
• Co-emulsifier that helps keep oil-and-water formulas stable
• Skin-identical fatty acid with a soft, smoothing emollient feel

Side effects

• Mildly comedogenic (commonly rated around 2-3/5), so it may contribute to clogged pores in those prone to them
• Soap-based cleansing from stearic acid can be drying for some skin
• Sits within the C11-C24 fatty-acid range that lipid-dependent Malassezia yeast can feed on, so it is generally flagged as a potential fungal-acne (Malassezia folliculitis) trigger

Who it's for

Most skin types; mainly a texture/emulsifier ingredient rather than an active

Who should be careful

Very acne-prone or fungal-acne (Malassezia folliculitis)-prone skin may want to limit fatty-acid-heavy products