Serums! You’ve heard of ‘em, you've seen ‘em, but uh...you’re not exactly sure what they do. And you sure as heck have no clue which one is right for you. Well, friends, rejoice. The following 700 or so words were constructed just for you.

Technically speaking, a serum is a thin substance that’s applied before moisturizer and sunscreen. Its ingredients are concentrated and engineered to target specific skin concerns (like dullness, acne, uneven texture, the list goes on). Made for daily application, they are not to be confused with a weekly treatment (like a peel or mask), but they can sensitize skin, so make sure to always follow up with a liberal scoop of sunscreen. Although most serums are equipped with some amount of hydrating elements, they are not meant to replace a moisturizer altogether (well, hyaluronic acid serums CAN replace a moisturizer, but only if you have oily skin and you really, really want to avoid a cream). OK, that’s enough of a primer. Let’s get to trying.

The one to try RIGHT NOW (or if you have dry skin)

It’s January, and there’s no better time to hop to a hyaluronic acid serum than right now. Why, you ask? Because hyaluronic acid is the grandaddy of all humectants (feel free to brush up on the usefulness of humectants right here). It draws water to your skin more effectively than any other ingredient. Even better: it’s not heavy! That hydrating goo does more work than your heaviest moisturizer. Pestle & Mortar makes the Cadillac of hyaluronic acids (lightweight, non-sticky), but if you’re looking to spend less than 70 bucks, try Paula Choice’s slightly thicker-but-still-pretty-good version for half the price.

The antioxidant one

A lot of antioxidants out there, but the only one worth your time is vitamin C. (The other ones aren’t bad, you just get more bang for your buck with vitamin C.) It brightens, and it prevents and dissolves existing dark marks—so if you’ve got post-acne hyperpigmentation or sun spots, this one’s for you. The best formulations come in 15-percent and 20-percent concentrations, and are buffered with ferulic acid and vitamin E, which stabilize vitamin C (it’s otherwise extremely sensitive to light and air exposure), as well as maximize its brightening fire power. Skinceuticals is sort of the industry standard (but $$$), but Maelove’s Glow Maker is an impeccable dupe. A warning, however: If your skin leans on the sensitive side, slowly ease your way into daily use by starting out on a twice-weekly application schedule, first.

The one that makes your face super smooth

More acids! Only these don’t hydrate, they refine. If your skin texture is all over the place, or you just want to reap the benefits of a daily scrub (without actually scrubbing...), an alpha hydroxy acid serum is calling your name. The crowd favorite? Make that Sunday Riley’s Good Genes, whose lactic acid formulation makes your skin feel like the surface of an inflated balloon (a good thing!). Other options: First Aid’s FAB Skin Lab Resurfacing Liquid (includes 10-percent alpha hydroxy acids), Farmacy’s Honeymoon Glow, and the Drunk Elephant everyone can’t stop talking about.

The one for pimples

Here goes another acid serum (hey, they work!). This time you want to look for ingredients like beta hydroxy acid, which makes your pores nice and clear, or azelaic acid (an increasing favorite amongst the ITG crew, and works similarly to BHA). A few options: Renée Rouleau’s BHA Clarifying Serum will have your face cleared up in no time, and PCA Skin’s Acne Gel winning combination of both beta hydroxy acid AND azelaic acid is the dream team equivalent of an acne serum. Or if you just want to keep it simple, try Paula Choice’s Azelaic Acid Booster—straight to the point and Tom’s favorite.

The one to try if you have fine lines

Retinol! Still the best OTC wrinkle-reducer in these streets (it also smooths skin, kind of like an alpha hydroxy acid, but better…). The only downside is that it takes a least two months, but usually around three, to start noticing any effect. Some options to add to your cart: Obagi’s 1% retinol formula, Replenix’s .3% retinol, and Dr. Brandt’s 2% Retinol Complex Serum. And for goodness sake, don’t forget to follow up with sunscreen.

Photo via ITG