Hair Oil vs Serum: Differences, Benefits, & How to Use Both

Hair oils and serums share some common traits. Both can add shine, smooth frizz, and make hair feel softer—and that’s where the confusion usually starts. Everyone ends up thinking they do the same job and deliver the same results (and the nearly identical packaging doesn’t make matters any better!)

But there’s another layer to this misunderstanding. Too often, many treat it as an either-or choice instead of considering how they might work together for even better results. Spoiler: they can, and they do!

In this guide, we walk you through the key differences between hair oil and serum, when to use each on its own, and how to combine them the right way so your hair feels light, healthy, and styled without being overloaded.

What Hair Oils and Serums Are

Before we go into their differences, here’s a quick look at what each one actually is.

What Is Hair Serum?

A hair serum is a lightweight product, often made with silicones, plant oils, or a mix of both. It coats the surface of the hair to change how it looks and feels right away.

In other words, it’s what you reach for when you want instant shine, smoother strands, or softer ends without waiting for long-term results.

Although, some serums do go beyond cosmetic fixes. They can include active ingredients that, with regular use, help support healthier hair growth. In fact, a peer-reviewed clinical study in 2020 found that a multi-ingredient hair serum, applied daily for 90 days, improved hair growth rate and density in adults with hair fall.

What Is Hair Oil?

Hair oil is a nutrient-rich liquid made from plant-based oils or blends of essential oils. It works deeper than the hair’s surface, often starting at the scalp and running through the lengths to nourish, protect, and condition over time.

And this isn’t just a casual claim. A study published in the Journal of Cosmetic Dermatology found that products with essential oils are well-suited for scalp care because of their antimicrobial and anti-inflammatory benefits. These qualities make them especially helpful for dryness, flaking, or mild irritation.

That's to say hair oil isn’t a quick-fix product. It’s something you use regularly to lock in moisture and maintain a healthier scalp and hair over the long term.

Key Differences Between Hair Oil vs Serum

Earlier, we defined hair oil as something that works deeper, often starting at the scalp, while hair serum mainly targets the surface for quick, visible results—that’s the big-picture difference. However, note that they also differ in other important ways.

Formulation or Ingredients

Hair oils are usually made from pure plant oils or blends of essential oils, with little to no added water. They feed your hair and scalp with fatty acids, vitamins, and antioxidants.

Take raw batana oil, for example. It’s loaded with oleic acid, palmitic acid, and vitamin E—nutrients that help repair damage, improve softness, and keep the scalp healthy. Another well-known option, argan oil, contains linoleic acid and squalene, which help smooth the hair cuticle and add a natural shine.

Hair serums are different. They’re usually a mix of water, silicones or lightweight oils, and active ingredients aimed at smoothing, sealing, or protecting the hair cuticle. Put differently, their job is to coat the hair, not sink deep into it.

Weight & Texture

Oils range from light and runny to thick and viscous, depending on the plant source. For example, coconut oil is on the thicker end, while jojoba oil sits on the opposite side with its lighter, more fluid texture.

That said, they can feel richer and more nourishing but may weigh hair down if overused.

Serums, on the other hand, are generally lighter and more slippery, designed to coat without feeling heavy.

Timing in Routine

Hair oils are often applied before washing as a pre-treatment (usually overnight for deeper nourishment). Serums, meanwhile, are usually applied after styling or on towel-dried hair for a polished finish.

Later on, you’ll see how both fit into the full routine, from washing in the shower to drying and styling.

Absorption & Longevity

Oils can work their way into the hair shaft to carry nutrients and moisture into the inner layers. As a result, the conditioning effect can last through several washes.

Serums work differently. They stay on the hair’s outer cuticle, giving a smooth, glossy finish and shielding against stressors like humidity or heat. Since they don’t usually reach the inner layers, the effects fade sooner and may need reapplication to keep the look.

Which is Better for Hair, Serum or Oil?

There’s no outright “better” between the two since each serves a different purpose. Hair oil supports long-term scalp and hair health, while hair serum delivers quick cosmetic results. All that’s to say the better choice depends on when and why you’re using it—and that usually comes down to lifestyle and routine. Here's a quick guide:

Use hair oil when:

• You’re dealing with ongoing issues like dryness, brittleness, thinning at the crown, or split ends, and you want gradual improvement over weeks or months.

• You want to keep hair healthier over time by nourishing the scalp and locking in moisture before damage happens.

• You have time to prep—such as before bed, on a self-care evening, or as a pre-wash treatment—so the oil can absorb fully.

Use hair serum when:

• You need a quick touch-up before heading out, whether for work, errands, or a night out.

• You style with heat tools often and want an extra layer of protection that coats the hair shaft to reduce damage.

• You’re active at the gym or outdoors and want a light product that won’t make your hair feel greasy if you sweat.

Can I Use Both Hair Serum and Hair Oil?

Yes, you can use both. The key is to follow an order that lets each product work as it should. Here’s a simple routine that does just that:

1. Pre-wash oiling: Massage oil into your scalp and work it through the mid-lengths to ends. Leave it for at least 30 minutes, or overnight if you want deeper nourishment.

2. Wash hair: Shampoo and condition as usual to clean your scalp and remove excess oil.

3. Towel-dry gently: Blot, don’t rub, to avoid breakage. Stop when hair is about 80% dry—still slightly damp but not dripping. This is when hair takes in serum best because the cuticle is still partially open.

4. Apply serum: Warm a few drops between your palms and smooth over mid-lengths and ends. Skip the roots unless you’re using a scalp treatment serum. Comb through for even coverage.

5. Finish drying: Air-dry for a natural look or blow-dry if styling. If you use heat tools, pick a serum with heat-protective properties.

There’s no rule that says you have to choose one over the other. Whether your hair is curly, straight, thick, fine, frizzy, or color-treated, both can fit into your routine when used with intention.

Do You Put Hair Oil or Serum First?

As a general rule of thumb, apply hair oil first, then follow with hair serum. The reason is that oil works to nourish the scalp and penetrate the hair shaft, while serum coats the outer layer for protection and a polished finish.

What happens otherwise? Putting oil on after serum can block its ability to absorb fully. Most of it ends up sitting on top instead of reaching the inner layers.As a result, you’d notice more of the oil’s texture and weight on the outside. That leaves your hair looking greasy or heavy without giving the deeper conditioning you were aiming for.

How Often Should You Use a Hair Oil or Hair Serum?

For hair oil, how often you should use it depends on your hair type. Many users apply it daily without issues and see great results, though most find the sweet spot of around two to three times a week. However, if your scalp happens to be naturally oily, consider using it less, about once every week or two, to avoid a heavy or greasy feel.

Hair serum, on the other hand, works well for daily use. It’s especially handy if you style your hair often or want to keep flyaways under control.

Hair Oil vs Serum: Does the Difference Matter?

At the end of the day, it’s about taking care of your hair and feeling good about how it looks. When you think about it that way, it’s not the difference but the combination that matters most—serum for styling and oil for deeper nourishment.

That said, if you had to choose where to start, we suggest going with hair oil. A good one works into your hair over time to make it stronger and help prevent dryness, breakage, or thinning—problems we want to deal with sooner than later.

And speaking of hair oils, there’s plenty more to know about which ones truly support growth and why making oiling a habit can change your hair for the better. We cover this in detail on the Keyoma blog. So definitely check that out when you’re ready to take the next step in your hair care routine.