Facial Serum vs. Facial Moisturizer: What's the Difference?

From toners and cleansers to creams and essences, we'll be the first to admit that the sheer number of skincare products available can be dizzying. Throw in skin type considerations and seasonal shifts, and we're often left scratching our heads wondering what our skin actually needs. Most people have serums and moisturizers on constant rotation, but do you really need to be using them both? Should we be using a serum before or after moisturizer? What's the difference between the two?

To dive into these questions and more, we called on three board-certified dermatologists for some answers. Ahead, they break down the differences between these two products along with how to integrate them into your routine.

What Is Face Serum? 
"Serums are typically lightweight formulations that deliver actives," explains Hartman. "They are usually thin and absorbent, leaving little, if anything, remaining on the surface of the skin." And because they don't have a strict definition, a serum may technically be a lotion, gel, or oil. Serums also tend to address a variety of skin concerns, be it anti-aging, skin brightening, or acne prevention. Though they tend to be more expensive than other skincare products, they're full of potent ingredients and a little goes a long way. With that said, Robinson advises to always ask your dermatologist which serums are best to apply at night and during the day.

What Is Moisturizer? 
"Moisturizers use a thicker formula to create a physical barrier that locks in hydration and prevents skin from drying out," says Robinson. "Additionally, they can enhance the functioning of the stratum corneum (the uppermost layer of skin that's made up of fat and oil skin cells) to help retain moisture."
Some moisturizers have added anti-aging ingredients, so they do double duty for your skin. But in order to really address a difficult skincare problem (think: sun damage), you may want to combine your moisturizer with a quality serum. 

Face Serums vs. Moisturizers: The Key Differences 
We've uncovered that serums are thinner and lighter, whereas moisturizers have a thicker, creamier consistency. But what about how they perform? "Serums are intended to penetrate deeply into the skin to deliver targeted active ingredients, whereas moisturizers help to fortify the surface of the skin, bind skin cells together more effectively, and work at the surface of the skin to increase hydration," says Hartman. Moisturizers also may have larger molecules than serums. This means that a moisturizer usually won't penetrate the skin as deeply, or as quickly, as a serum will. This can be a double-edged sword: If you're looking for strong effects, you should be relying on your serum, but if you're looking for continuous hydration, that's your moisturizer's job.

Can You Use Serums and Moisturizers Together? 
González says that layering the two is really all about the products themselves, their ingredients, and your skin type. "For example, layering a serum and moisturizer can be very helpful for those with very dry skin," she explains. "The serum will help deliver any active ingredients, and the moisturizer will help lock in moisture in the skin, seal in the serum, and help potentiate its active ingredients." That said, if you have acne-prone skin, it may be best to avoid an oil-based serum.
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How to Layer Serums and Moisturizers 
When it comes to layering skincare products, order matters. "In general, skincare products are layered from thinnest to thickest with the thinnest products being applied to the skin first. If you think about the intended goals, it makes sense. Serums are intended to deliver active ingredients deep into the skin and the moisturizer forms a seal to make the serums more efficacious," explains Hartman.
To effectively layer your serum and moisturizer, first rub the serum onto your face and neck. Then, wait 30 to 60 seconds before applying your moisturizer on top. "The reason for waiting is that you want the serum to settle in before you apply the moisturizer," notes González.

​While most serums and moisturizers are used both in the morning and evening, there are some serums or creams that should only be used at night depending on their ingredients. Be sure to read the instructions on the products you are using to find out which you should use in the morning and which you should use at night. And as always, consult with your dermatologist if you're in any way unsure."