Isopropyl Myristate
In plain terms
A light, silky ester used to make creams and makeup glide and absorb fast. It is safe on the skin's terms, but two traits make it depend on your skin: it is strongly pore-clogging, and it helps other ingredients penetrate deeper.
What the evidence shows
Isopropyl myristate is a lightweight ester that gives lotions and makeup a dry, fast-absorbing, non-greasy slip, which is why it is in so many products. On straight safety it is well cleared: the US cosmetic-ingredient panel judged it non-toxic, non-irritating, and non-sensitizing up to high concentrations. Two functional traits are what land it at depends. First, it is one of the more pore-clogging cosmetic ingredients, scoring near the top of the comedogenic scale; it works its way into the follicle, mixes with sebum, and can trigger the plugging that forms whiteheads and blackheads, so dermatologists routinely flag it for acne-prone skin. Second, it is a penetration enhancer: it loosens the skin barrier to help actives sink in, which is useful by design but also means it can carry other, less welcome ingredients deeper than they would go alone. Neither trait is a toxicity concern, and for skin that is not acne-prone it is a pleasant, well-tolerated emollient. Whether it suits you depends on how breakout-prone your skin is and what it is paired with.
On the label
Listed as isopropyl myristate or IPM, common in fast-absorbing lotions, makeup, and cleansing products. If your skin is acne-prone, this is a reasonable one to limit, since it sits high on the pore-clogging scale; it also boosts how much of the rest of the formula your skin takes up.