If there's one skincare step I really adore, it's serums. No matter which skin type you have, you can benefit from a good serum. I know there's some debate on weather you should use them or not, but I believe it makes a difference. Especially if you are using a moisturizer that doesn't contain all the ingredients you want to use. As you apply the serum before moisturizing, the moisturizer ''locks in'' the serum so the skin can use all the ingredients well. Even if your skin is oily or combination you can find a serum that works for you. I have combination skin  and like to use a moisturizer that is mattifying and has a SPF in the morning so I actually get all the moisture for my skin from the serum. Keep on reading to see which serums I recommend for different skin types. I've tested all of these by myself, so I'm not just talking without a lot of information!

Oily and acne prone skin

By far the hardest skin type to have when it comes to looking for new products. You never know what will break you out and are constantly trying to find something that actually fights the acne. I find that when you have a problem with acne, it's the best to avoid too much moisturizing or even ingredients that are to harsh. You should go for serums with salicylic acid or similar active ingredients. I've recently tried Mr. Black Anti acne serum and although it comes in a set of three products, I find it's quite effective on its own as well. It's a light liquid so the skin absorbs it super fast. The active ingredient in in is salicylic acid.

Dry skin

If your skin is only dry and you have no other issues, like sensitivity, eczema or acne it's enough to keep it hydrated and ''double hydratation'' with both a serum and a moisturizer is a good idea. I'm all for hyaluronic acid serums. I've tried some excellent ones in the past, right now I'm really loving Ordinary Hyaluronic acid 2% + B5. Great thing about it is that it moisturizes really well, but is light as well so it won't interfere with other products that you are using.

Normal to combination

One brand I discovered about a year ago is making some of the best serums I've ever tried. They are all from the Serumdipity line from a brand called Azelique. I've never heard about it before, until I found it on iHerb. I don't know if you can buy it anywhere else, I always get it from iHerb. 
This is the serum I'm using right now, mainly as my daytime serum (but I sometimes use it at night), Azelique Serumdipity Anti-aging Vitamin C facial serum. I'm not sure whether you really get the benefits of the vitamin C part, but it moisturizes perfectly while being super light. And it never broke me out, which is sometimes possible with oily skin.

Mature skin

My skincare philosophy is to not use collagen or other similar ingredients until your mid-twenties, because the skin is effectively producing it while you are younger. When you feel like your skin needs it, it's great to start with serums that contain collagen. This one is from the same brand as the previous serum I mentioned, Azelique Serumdipity Anti-aging Collagen facial serum. I've got it just to try it out, and it's a bit thicker than the Vitamin C serum and makes the skin smoother and softer.

Wrinkles and pigmentation

Over the night serums are great for targeting skin issues like pigmentation, wrinkles, acne scars and other spots. 
I am a huge fan of Alpha H liquid gold lotion and I really like the Alpha H Concentrate with Hexapeptide. These type of serums are actually treatments and you should only use them couple times a week. I like to use this one once a week. It's recommended not to use moisturizer after this treatment so it will work more efficiently.