Scalp serums explained: niacinamide, salicylic acid, caffeine and more

Scalp serums have moved from the back of the pharmacy shelf to the front of skincare counters. Many now borrow the language of face care: niacinamide, salicylic acid, peptides, "barrier repair", "exfoliating" and "balancing". Some promise less hair fall, some promise a calmer, less oily scalp, and some promise both. The ingredients on the label range from well-studied to barely studied, and a few can irritate the scalp they are supposed to help. This guide explains what the most common scalp serum ingredients are meant to do, what the evidence actually shows, and how to choose a serum that matches your scalp problem rather than the marketing.

(This is general information, not personal medical advice.)

Short answer

A scalp serum is a leave-on product, so its ingredients stay on the skin for hours, and what it can do depends on those ingredients. Niacinamide (a form of vitamin B3) appears in many serums; a small six-month trial of two niacin derivatives found a modest increase in hair fullness in women with pattern hair loss, while a laboratory study found that topically applied nicotinamide inhibited the growth of human hair follicles kept alive outside the body ¹, ². Salicylic acid loosens scale and is a recognised dandruff and scalp psoriasis ingredient, not a hair growth treatment ³, ⁴. Topical caffeine has a growing but mostly low-quality body of clinical evidence ⁵. Minoxidil remains the topical ingredient with the strongest evidence for pattern hair loss ⁶, ⁷. Fragrance and some preservatives are common scalp allergens ⁸. Choose a serum for a specific problem, and see a doctor if hair loss is the main concern.

What makes a serum different from a shampoo or tonic

A shampoo is rinsed off after a minute or two, so its active ingredients have limited contact time with the scalp. A serum is applied to the scalp and left on. That has two consequences. First, an active ingredient has more time to act. Second, any ingredient that irritates or sensitises the scalp also has more time to do so.

The terms "serum", "tonic", "essence" and "ampoule" are not standard categories. They describe texture and marketing more than function. A water-based serum with alcohol may behave much like a tonic; a serum with oils and silicones may behave more like a leave-in conditioner. For a comparison of these formats, see Hair growth serums: which ingredients have evidence behind them.

In Malaysia, most scalp serums without a medicine in them are sold as cosmetics. Companies must notify the National Pharmaceutical Regulatory Agency (NPRA) before a cosmetic is manufactured, imported or sold ⁹. A notification number shows that a product has been notified as a cosmetic. It does not mean the agency has tested whether it reduces hair loss.

Niacinamide and other forms of vitamin B3

What it is meant to do

Niacinamide (also called nicotinamide) is one of the most popular ingredients in face skincare, where it is used for oil control, redness and barrier support. Scalp products use it for similar reasons: to calm the scalp and, in some marketing, to "strengthen roots" or "reduce hair fall".

What the evidence shows

The scalp evidence is limited and mixed.

• A 2005 pilot study gave 60 women with pattern hair loss either a lotion containing two niacin derivatives (octyl nicotinate and tetradecyl nicotinate) or a placebo. After six months, blinded photographic analysis showed a statistically significant increase in hair fullness in the active group. The authors called it promising and said it warranted further study ¹. Note that these are niacin esters, not the niacinamide found in most serums.
• A 2018 laboratory study by hair follicle researchers reported that topically applied nicotinamide inhibited the growth of human hair follicles kept alive in the laboratory (ex vivo) ². Laboratory results do not always predict what happens on a living scalp, but this is a reason not to assume niacinamide is automatically good for hair growth.
• A 24-week placebo-controlled trial sponsored by a consumer products company tested a shampoo and leave-on regimen containing several ingredients together: piroctone olamine, zinc pyrithione, zinc carbonate, niacinamide, panthenol and caffeine. People with self-perceived thinning had less hair shedding and a higher total hair count than with the placebo shampoo, along with improved scalp barrier measures ¹⁰. Because the ingredients were tested as a combination, the result cannot be credited to niacinamide alone.

Practical view

Niacinamide is generally well tolerated in skincare and may help some people with a sensitive or oily scalp feel more comfortable. There is not enough evidence to treat a niacinamide serum as a hair loss treatment.

Salicylic acid

What it is meant to do

Salicylic acid is a keratolytic, meaning it softens and loosens scale so it can be washed away. On the scalp it is used to reduce flakes and build-up.

What the evidence shows

The American Academy of Dermatology lists salicylic acid among the active ingredients to look for in dandruff shampoos, alongside zinc pyrithione, sulfur, selenium sulfide, ketoconazole and coal tar ³. DermNet lists salicylic acid among the keratolytic (anti-scaling) agents used for scalp psoriasis, and notes that salicylic acid shampoos can enhance the penetration of other topical treatments, including corticosteroids ⁴.

A small study of 20 people with moderate to severe scalp seborrhoeic dermatitis used a pre-wash gel and a cleanser that both contained salicylic acid and piroctone olamine, among other ingredients. Dandruff, itch, redness and greasiness scores fell over four weeks ¹¹. The study had no control group and the products combined several ingredients, so it shows feasibility rather than proof.

Practical view

Salicylic acid is useful when the problem is flaking, scale or build-up. It does not treat pattern hair loss. Leave-on salicylic acid can sting or dry the scalp, especially if the skin is broken or already irritated. If you have thick, stuck-on scale, persistent redness or itch, see a doctor, as the cause may be seborrhoeic dermatitis, psoriasis or a fungal infection that needs specific treatment ³. See Seborrhoeic dermatitis of the scalp: more than dandruff and Scalp psoriasis: signs, triggers and treatment basics.

Caffeine

What it is meant to do

Caffeine is marketed as a follicle "energiser". In the laboratory, caffeine has been shown to counteract some effects of testosterone on hair follicles grown in culture ¹², and studies suggest it can penetrate into hair follicles when applied to the scalp ¹³.

What the evidence shows

A 2025 systematic review found nine clinical trials of topical caffeine products, involving 684 people with androgenetic alopecia, excessive hair loss or thinning. All concluded in favour of caffeine, but the quality of evidence was medium in three studies, low in one and very low in five. Common weaknesses were a lack of randomisation, a lack of placebo or control groups, and missing information on caffeine concentration. The reviewers said caffeine products may be worth a try but better trials are needed ⁵.

One open-label randomised study in 210 men compared a 0.2% caffeine liquid with 5% minoxidil solution over six months and reported similar improvements in the proportion of growing (anagen) hairs ¹⁴. It was not blinded, and it measured one specific outcome.

Practical view

Caffeine is a reasonable cosmetic option with a low risk profile for people who do not want, or cannot use, minoxidil. It should not be expected to match proven treatments on the strength of current evidence.

Peptides

Copper peptides and other signal peptides appear in many premium serums. A laboratory study found that a tripeptide-copper complex increased the growth of human hair follicles in culture ¹⁵. Clinical trials in people are limited. Peptides are generally gentle on the skin, but there is little evidence that they meaningfully change hair loss.

Rosemary and other plant extracts

Rosemary oil became popular after a six-month trial in 100 people with androgenetic alopecia. Both rosemary oil and 2% minoxidil groups showed a significant increase in hair count at six months but not at three months, with no significant difference between groups. Scalp itching increased in both groups, more often with minoxidil ¹⁶. This is a single trial, using 2% rather than 5% minoxidil. Plant extracts in serums are often present at unknown concentrations, and essential oils and fragrance can cause allergic reactions. See Rosemary oil for hair growth: a closer look at the evidence.

Antidandruff actives in serums

Some scalp serums contain zinc pyrithione, piroctone olamine or ketoconazole, which are better known from dandruff shampoos. These ingredients target the yeasts linked to dandruff and seborrhoeic dermatitis. A systematic review of topical ketoconazole in androgenetic alopecia found human studies reporting increased hair shaft diameter and called it a promising adjunctive or alternative therapy, while noting that randomised controlled trials are still needed ¹⁷. If dandruff or an oily, itchy scalp is part of your problem, a product with one of these actives may be more useful than a serum built around trendier ingredients. See Dandruff treatment: a step-by-step guide.

Minoxidil: the benchmark

Minoxidil is the topical ingredient with the strongest evidence for pattern hair loss. Minoxidil 5% foam and 2% and 5% solutions are approved for androgenetic alopecia, and results need at least four months of use to assess ⁶, ⁷. A product that contains minoxidil is a medicine and should list it as an active ingredient with its strength. If your main goal is to slow pattern hair loss, compare any serum against this benchmark. See Minoxidil in Malaysia: forms, strengths and buying it sensibly.

Ingredients that can cause problems

A systematic review of scalp allergic contact dermatitis found that the most commonly reported patch test allergens from scalp and hair products included p-phenylenediamine (mainly in hair dyes), nickel, fragrance mix, balsam of Peru, cocamidopropyl betaine and methylchloroisothiazolinone/methylisothiazolinone. Typical signs were eczema-like patches, itch and burning ⁸. In leave-on serums, the ingredients most worth checking are:

• fragrance (parfum) and essential oils, a frequent cause of allergy
• preservatives such as methylisothiazolinone
• alcohol, which helps a serum dry quickly but can sting or dry a sensitive scalp
• acids, including salicylic acid and glycolic acid, which can sting broken or irritated skin

If a serum makes your scalp itch, burn, or turn red or flaky, stop using it. Persistent symptoms deserve a doctor's look.

Matching a serum to your scalp problem

How to use a scalp serum sensibly

• Apply to the scalp, not the hair. Part the hair and apply to the skin where the product is meant to act.
• Patch test first if you have sensitive skin. Try a small area for a few days before using it widely.
• Use one new product at a time. If a reaction happens, you will know which product caused it.
• Follow the directions on frequency. More is not better, particularly for acids.
• Give it time. Scalp comfort may change within weeks; hair changes take months.
• Take photos. Photos taken in the same light every month are more reliable than memory.

When to see a doctor

See a doctor if:

• you are losing hair quickly, in patches or with a widening part
• your scalp is red, painful, scaly or weeping
• flakes or itch continue despite an antidandruff product
• a serum causes a reaction that does not settle after you stop it
• you are unsure whether your hair loss is pattern loss, shedding or a scalp disease

Life in Malaysia

Scalp serums sold in Malaysia include local brands and imports from Korea, Japan, Taiwan, Europe and the United States, sold in pharmacies, beauty chains and online marketplaces. Hot, humid weather and sweat can make heavy, oily serums uncomfortable and may worsen an irritated scalp, so lightweight, fragrance-free formulas are often easier to use daily. If you wear a hijab or cap for long hours, allow a serum to dry before covering the hair. For scalp care in local weather, see Scalp care in Malaysia's hot, humid weather. For a sensible way to deal with build-up, see Scalp detox: what it means, what it does not, and a sensible version. If you are buying from a pharmacy, see Hair loss products at the pharmacy: what to ask the pharmacist. If you see a doctor, choose a registered practitioner; you can check registration with the Malaysian Medical Council ¹⁸. For an overview of treatment options, see Hair loss treatment in Malaysia: a plain guide to your options.

Bottom line

Scalp serums are best chosen by ingredient and by problem. Salicylic acid and antidandruff actives help with flakes, scale and an oily scalp. Niacinamide and peptides may make a scalp feel more comfortable, but their evidence for hair loss is thin, and one laboratory study found nicotinamide inhibited follicle growth. Caffeine has more clinical studies, mostly of low quality. Minoxidil remains the benchmark for pattern hair loss. Avoid unnecessary fragrance on a sensitive scalp, introduce one product at a time, and see a doctor if the main problem is hair loss rather than scalp comfort.

Frequently asked questions

Does niacinamide help hair loss?

The evidence is limited and mixed. A small trial of two niacin derivatives found a modest increase in hair fullness, while a lab study found topical nicotinamide inhibited human hair follicle growth ex vivo.

What does salicylic acid do on the scalp?

It loosens and softens scale so it can be washed away. It is used for dandruff and scalp psoriasis, not as a hair growth treatment.

Do caffeine scalp serums work?

A 2025 systematic review found nine clinical studies that all favoured caffeine, but most of the evidence was low or very low quality. Better trials are needed.

Is a scalp serum better than minoxidil?

Minoxidil has the strongest evidence of any topical ingredient for pattern hair loss. Cosmetic serums have weaker evidence.

Can scalp serums cause irritation?

Yes. Fragrance, some preservatives, alcohol and acids can irritate or cause allergy, and a leave-on product stays on the skin for hours.

Does a notification number mean a serum works?

No. In Malaysia, a notification number means the product has been notified to NPRA as a cosmetic. It does not mean it was tested for reducing hair loss.

How long should I try a scalp serum?

Scalp comfort may change within weeks, but hair changes take months. Minoxidil, for example, needs at least four months to judge.

When should I see a doctor instead of buying a serum?

If hair is falling out quickly or in patches, if the scalp is red, painful or scaly, or if flaking persists despite antidandruff products.

Educational content. Not medical advice.