Comedogenicity

Comedogenicity is the tendency of an ingredient or product to clog pores and contribute to the formation of comedones, the blackheads and whiteheads that are early stages of acne. An ingredient described as non-comedogenic is one considered less likely to cause this clogging.

A comedone forms when sebum and dead skin cells build up within a follicle. Certain oils, waxes and heavy emollients are thought to increase the chance of this happening, especially on acne-prone skin. Historically, ingredients were ranked on comedogenicity scales, but these ratings have important limitations: many came from animal-model testing at high concentrations, they do not account for how much of an ingredient is present, or how it behaves once blended into a finished formula.

The practical implication is that comedogenicity is best treated as a rough guide rather than a fixed rule. A single "comedogenic" ingredient low down in an ingredient list may cause no problem, while overall texture, occlusiveness and individual skin response matter as much as any list. Because reactions are so personal, patch testing a new product and observing how skin behaves over a few weeks is more reliable than relying on ingredient ratings alone.