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Why oxidised sebum, not sebum, clogs pores

Oxidised squalene was more pore-clogging than well-known comedogenic cosmetic ingredients, while unoxidised squalene was not — which is the reason the stable form exists.

Researchers applied squalene, oxidised squalene, and the reduced form of oxidised squalene to rabbit ear skin and compared how much follicular plugging each caused. Oxidised squalene produced more plugging than cosmetic ingredients already known to be comedogenic. Plain squalene, and the reduced form, produced much less. The relevance to squalane is indirect but important. Squalene is a large part of your own sebum, and UVA light turns it into these peroxides on the skin surface. Squalane is squalene with all its reactive double bonds filled in, so it cannot form them. That is the chemical argument for using the stable version in products, and it is why the common claim that "squalene causes acne so avoid squalane" has the logic backwards.

Chiba K, Yoshizawa K, Makino I, Kawakami K, Onoue M. Comedogenicity of squalene monohydroperoxide in the skin after topical application. J Toxicol Sci. 2000;25(2):77-83.