Sebum was collected from the faces of seventeen healthy volunteers and exposed to UVA or UVB light, with the resulting chemicals identified by laboratory analysis. UVA depleted the squalene in sebum and generated squalene peroxides in its place, and it did so even at doses too small to redden skin. Before exposure, peroxide levels were barely detectable. Read alongside the comedogenicity work, this completes the picture: ordinary daylight converts the squalene on your skin into a form that is strongly pore-clogging. It also draws a boundary worth knowing. Applying squalane does not prevent your own squalene from oxidising. Squalane is a stable oil to put on skin, not an intervention against this process.
Ekanayake Mudiyanselage S, Hamburger M, Elsner P, Thiele JJ. Ultraviolet A induces generation of squalene monohydroperoxide isomers in human sebum and skin surface lipids in vitro and in vivo. J Invest Dermatol. 2003;120(6):915-922.