Rosemary for hair: oil, extract, water and serum compared

Rosemary reaches hair care in four main forms: the pure essential oil, the essential oil diluted in a carrier oil, homemade rosemary water, and rosemary extract in a ready-made serum. They come from one plant but behave very differently on a scalp. The right one depends on whether you want a wash-day ritual or a daily leave-on step, and on how your hair responds to oil.

Rosemary has become one of the most talked-about plants in hair care, and most of the talk treats it as a single thing. It is not. This guide sets out the four forms side by side, what each is made of, how to use it, and what the research does and does not say. Where we have gone deeper on a question, there is a link.

At a glance

• Pure essential oil. Concentrated, fragrant, not for use neat on skin. Needs diluting.
• Diluted rosemary oil. Essential oil in a carrier oil such as jojoba or castor. A pre-wash treatment, shampooed out.
• Rosemary water. Leaves steeped or simmered in water. Light, but homemade and short-lived.
• Rosemary serum. Usually rosemary extract in a water-based formula. A leave-on step for a clean scalp.

1. Rosemary essential oil

The essential oil is made by steam distillation of the plant's aerial parts.¹ It is a small fraction of the plant, up to about 2.5 percent of the leaves by one review's figures, colourless to pale yellow, water-insoluble, and dominated by camphor, 1,8-cineole and alpha-pinene.²

It is not meant for use neat. The US National Cancer Institute notes that essential oils are most often applied to skin in a diluted form, and that allergic reactions and skin irritation may occur with long contact.³ The European Medicines Agency records contact dermatitis among rosemary oil's possible reactions and advises against using it on broken or irritated skin.¹

Best for: people who want to make their own diluted blend and are willing to patch test.

2. Diluted rosemary oil

Most bottles sold as "rosemary oil for hair" are this: rosemary essential oil diluted in a carrier oil. Read the list on the back, because the carrier is most of what goes on the scalp.

It is a pre-wash product. Oil does not dissolve in water and needs shampoo to come out,⁴ and left on, hair oils may interfere with styling because of their greasy texture.⁵ Applied before a wash and shampooed out, that stops mattering.

Best for: medium to thick hair, a slow wash-day routine, and anyone who enjoys a pre-wash ritual. More in rosemary oil before or after washing hair.

3. Rosemary water

Rosemary water is made at home by simmering or steeping rosemary in water, then straining it and using it as a rinse or spray. It has no oil, so it does not leave a film, and it costs very little.

Its weaknesses are practical. It contains no preservative, so it is a perishable liquid: make small batches, keep it in the fridge, and throw it away if it turns cloudy or smells off. It is also inconsistent from batch to batch, because the strength depends on how much rosemary went in and for how long. And water alone will not carry the compounds that dissolve in oil or in other solvents.

Best for: people who like a homemade step and are happy to make it fresh.

Same plant, four products. The base, oil or water, decides how each one behaves far more than the rosemary does.

4. Rosemary serum

A rosemary serum usually contains rosemary extract rather than the essential oil. Extracts are made with a solvent and carry a different set of compounds, including rosmarinic acid, carnosic acid and carnosol.² On the bottle, look for Rosmarinus Officinalis Leaf Extract; the oil appears as Rosmarinus Officinalis Leaf Oil.⁶⁷

Because an extract can be carried in water, a serum can be water-based: it goes onto a clean scalp, dries down, and leaves nothing on the hair to flatten it. It is also preserved and made to a consistent formula, which homemade rosemary water is not.

Best for: fine hair, oily scalps, daily use, and anyone who wants the step to happen after styling rather than before washing. More in rosemary serum or rosemary oil and rosemary extract and rosemary oil are not the same thing.

What the research says

There is published research on rosemary and hair growth. Most of it concerns the essential oil.

The study cited most often, from 2015, tested a rosemary oil lotion standardised to its 1,8-cineole content, in 100 men, over six months.⁸⁹ That is a specific preparation of the oil in a specific group of people. It is often quoted to sell products that are not that preparation, including extracts, waters and serums. When a product leans on a study, it is worth checking whether the study tested anything like that product.

There is also a legal line worth knowing. In the US, a product sold to restore hair growth is a drug, and the FDA names that as one of its own examples of a drug claim.¹⁰ Rosemary products sold as cosmetics, ours included, work on how hair looks and feels.

Using any of them safely

• Patch test any new rosemary product on the inner arm and wait a day.
• Never use essential oil neat on the scalp.
• Keep it out of your eyes, and away from broken or irritated skin.¹
• Stop if your scalp itches, stings or reddens.
• Ask a doctor about any product you are unsure of while pregnant or breastfeeding.

Choosing one

• You wash every few days and like a ritual: diluted rosemary oil, before washing.
• You like making things yourself: rosemary water, fresh and refrigerated.
• Your roots go flat or greasy easily: a water-based rosemary serum.
• You want a daily step that does not touch your styling: a water-based rosemary serum.

Ours

Our rosemary serum is the fourth kind: rosemary leaf extract leading the blend, in a water-based formula with no oils and no added fragrance. Its partner is a peptide serum for the evening.

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

For how a peptide serum compares, see peptide serum or rosemary: which one, or both.

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.