Why a scalp serum can make hair greasy, and how to stop it

A scalp serum usually makes hair greasy for one of four reasons: the formula contains oils or silicones, too much went on, it landed on the hair instead of the scalp, or it was layered onto a scalp that was already oily or full of dry shampoo. Each has a simple fix, and most of them take less product, not more.

It is a frustrating problem because a scalp serum is supposed to be the light option. People often come to one precisely because a hair oil flattened their roots, and then find the serum does the same thing. Sometimes that is the formula. More often it is the technique, and the technique is easy to change.

The short version

1. Check the list on the back. If plant oils or silicones sit near the top, the serum will coat hair like an oil does.
2. Use a few drops. Not a full dropper. Most of a head is covered by three or four rows.
3. Apply to the scalp, not the hair. Part the hair and put the drops on exposed skin.
4. Start from a clean, dry scalp, or at least one without layers of dry shampoo on it.
5. Give it a minute to dry down before you brush, touch or heat-style the roots.

Reason one: the formula

"Serum" is a commercial word, not a regulated one, so it does not tell you what is in the bottle. Some products called scalp serums are oils in all but name; others are water-based liquids. The only reliable way to tell is the list on the back.

Under US rules, a cosmetic's components above one percent are listed in descending order of predominance.¹ If water leads the list, the product is mostly water. If a plant oil, a mineral oil or a silicone such as dimethicone appears in the top few, expect a film.

That film is what those materials are for. A review of hair cosmetics in the International Journal of Trichology describes dimethicone as the most widely used silicone in hair care, adsorbing onto the hair surface, and notes that thick films of oil may leave an oily and heavy look to the hair.² On the lengths of dry hair, that can be the goal. At the roots of fine hair, it is the problem.

A note on glycerin, because it appears near the top of a great many water-based serums, ours included. Glycerin is a humectant: it attracts and holds water.³ In normal amounts it simply dries down. Formulators have long noted that humectants at high concentrations can leave a sticky, tacky feel,⁴ which is one more reason a few drops is the dose and a whole dropper is not.

Reason two: the amount

This is the most common cause, and the easiest to fix. A scalp serum is meant to reach skin, and skin does not need much. A full dropper squeezed onto the crown cannot all reach the scalp. Whatever does not reach it stays on the hair around it, and the hair around it is exactly the part you see.

Start with a few drops across the whole head. If your scalp feels covered after massage, that was enough. If it does not, add a drop or two next time, not more this time.

Reason three: the placement

Hair sits on top of the scalp and catches whatever lands on it. Dropping serum onto the top of the head and rubbing it around mostly treats hair.

The fix is to part the hair and apply along the exposed line of skin. Make a part, place drops along it, move about an inch over, part again, repeat. Three or four rows covers most heads. Then massage with the pads of your fingers for a minute or two, which moves the serum across the scalp rather than up the hair.

Most "greasy serum" problems are a serum that was put on hair. The scalp is the target, the hair is in the way, and a part is how you get past it.

Reason four: what was already there

The scalp is one of the oiliest areas of skin on the body. Sebaceous glands are particularly dense there, reaching 400 to 900 glands per square centimetre on the scalp and forehead, far more than on the limbs.⁵ Their output is strongly driven by hormones, androgens in particular.⁶ Some scalps are simply oilier than others, and the American Academy of Dermatology's advice is to wash based on how often hair gets dirty or oily: with straight hair and an oily scalp, that may mean shampooing every day.⁷

A serum applied to a scalp already carrying a day or two of sebum adds a layer to an existing layer. The result can look greasy even if the serum itself is light.

Dry shampoo complicates this further. The AAD's answer to whether dry shampoo cleans hair is direct: no, it just absorbs the oil.⁸ The oil and the powder both stay on the scalp until the next wash. Adding a liquid to that mixture tends to turn it into paste.

The fix is timing. Apply a scalp serum to a clean scalp where you can, on wash day or the morning after. If you are using dry shampoo between washes, put the serum on before the dry shampoo rather than after it, and let it dry down in between.

Smaller things that add up

• Touching the roots while it is still wet. Give it a minute or two to dry down before brushing or running your hands through.
• Heat straight after application. Blow-dry once the serum has settled, and lift the roots with the brush rather than flattening them.
• Using it on the lengths. A scalp serum belongs on skin. If your ends need something, that is a job for a conditioner or a hair oil, used on the ends.
• Doubling up. A scalp serum, a root spray, a leave-in and an oil all at once can overwhelm fine hair. Take one away and see which one it was.

What a scalp serum is for, and what it is not

A cosmetic scalp serum works on how hair and scalp look and feel. In US law, a product sold to restore hair growth is a drug, and the FDA uses that as one of its own examples.⁹ That limit applies to every serum on the shelf. What a good one can do is fit into the day without undoing the rest of it, and for most people that means a formula that leaves nothing on the hair to flatten it.

Ours

Both of our serums are water-based and contain no oils and no silicones. Both have glycerin high on the list, which is why the directions say a few drops.

Botanical serum

Max Density

Rosemary leads the blend: only water and glycerin come before it. Water-based, no oils, no added fragrance. Left on for at least one to two hours before washing, which makes it the morning serum. 2 fl oz.

See Max Density

Peptide serum

Max Growth

Five peptides, each one printed on the bottle, in a water-based serum with no oils and no added fragrance. Nothing to rinse out, which makes it the evening serum. 1 fl oz.

See Max Growth

If you are still deciding between a serum and an oil, rosemary serum or rosemary oil compares the two. And if you want to check any bottle yourself, what a water-based hair serum is, and how to tell from the bottle shows what to look for. If oil and flat roots arrived with a new baby, postpartum hair always greasy? has a routine built for very little time, and if the part itself is what shows, how to cover a wide part covers the styling side.

Eloura products are cosmetics. They are not intended to diagnose, treat, cure or prevent any condition. This article is general information about hair care and is not medical advice.