I urge everyone to bookmark that blog; it is always a fascinating tour of the weirder and wonderfuller places on our planet. And let me leave you with this simply jaw-dropping video of undulatus asperatus in action.
(A sunscreen with a physical block like titanium dioxide or zinc oxide can be applied last, after a serum or moisturizer.) Apply a serum next and, finally, moisturizer if you need it. Polis also recommends serums or sunscreens with moisturizers built in because they save time.
The biggest difference between a serum and a cream or lotion is what the formulation doesn't include. Serums leave out occlusive, or airtight, moisturizing ingredients such as petrolatum or mineral oil that keep water from evaporating. They also contain fewer lubricating and thickening agents, like nut or seed oils.