I think the hardest thing for anyone with oil-slick skin to understand is that moisturizer is still important. Sure, when you're a collagen-rich young thing you can get away with skipping it -- if your skin remains smooth and even. But trouble starts if you have acne issues, use exfoliants, or develop that dry, tight feeling and dry patches that make no sense in the face of your blinding surface shine.
Skin needs a balance of two things: adequate sebum and water. Oily skin has lots of sebum. But it doesn't mean it has lots of water. If it's looking dull and tired, chances are it needs water. If it feels a little slack, chances are it needs water. If you're exfoliating regularly, chances are it needs water. If it's feeling dry and tight even though it doesn't look it, it definitely needs water.(I had a bridal client who had this problem -- oily skin, but always dry and uncomfortable. She was using rich creams for dry skin which were making her skin more oily, and causing breakouts, too. I suggested she switch to a just-hydrating line of products. Within weeks she reported major improvement, and had soft, glowy skin on her wedding day.)
Blemish-prone skin may have other issues, but if you're using a glycolic-acid toner, and you notice soon after cleansing and toning that your skin feels coated in grease, you. need. a. hydrating. moisturizer.
A hydrating moisturizer is all about giving thirsty skin what it needs: water, and a way to hang onto it. That last bit is important too: a way to hang onto it. Oily skin sans sufficient hydration is lacking something that helps keep moisture in -- some kind of natural lipid. And guess what? A natural lipid is a type of oil. Mother nature has a twisted sense of humour.
The best moisturizers for oily skin are light lotions, gels or gel-creams. Their packaging features words like "for dehydrated skin" or "hydrating." The line I recommended to the client I mentioned earlier is Vichy Aqualia Thermal -- it's specifically for dehydrated skin.
Right now I'm really enjoying StriVectin Instant Moisture Repair ($68), a light lotion powerhouse of peptides, nut and seed oils (to help skin's natural moisture barrier keep water in), sodium hyaluronate and squalane. Also key is the formula's use of "osmolytes," molecules that move water from cell to cell to help them maintain their volume and liquid balance. Remember high school science class, and the word "osmosis"? The movement of water through a porous barrier from a place of plenty to a place of not enough? In this formula, osmolytes -- agents of osmosis -- start work at the surface of the skin, drawing in moisture from the environment and transporting it beneath the surface for deeper hydration.
And you thought science class was a waste of time.
Properly hydrated oily skin glows like you wouldn't believe, by the way. In a good way.