How to REALLY fix your itchy scalp: The Science

Your scalp’s itchy and inflamed – and none of the products you’ve tried seem to be working. And now, maybe your hair’s even thinning.

Here’s the problem: Most scalp products aren’t treating the right cause, and no one’s really explaining what that is. And a lot of scalp products actually make things worse.

I’m the owner of a problematic scalp, and I used to scratch it raw. It took me years of going through the research, and trying different products, before I worked out what was really going on.

Let’s dive into the real science behind itchy scalp, and how to fix it for good.

The video version is here, keep scrolling for the article…

What causes itchy scalp?

There are three major causes, which all need to be treated differently. If you don’t get this right, a product might work for a while… but then you get itchy again.

Microbes

First, we need to talk about microbes.

Now, you might be thinking: I’ve heard Malassezia yeast causes dandruff, but my scalp’s just itchy – I don’t have flakes. But microbes are one of the most misunderstood causes of itchy scalp!

Malassezia is on everyone’s scalp, and it’s beneficial when everything is balanced. It helps keep more harmful microbes in check (try not to think too hard about all the microbes). But when the microbes are out of balance – when this yeast overgrows – that’s when things go wrong.

The problem comes from Malassezia feeding off sebum (your natural scalp oils) and turning it into irritating substances, such as:

This happens even without dandruff flakes! In one recent study, inflammatory markers rose after 3 days and people reported itching, but it took 3 weeks to see more flakes. So a lot of people don’t realise microbes are part of their problem, because they don’t have flakes yet (this was me!).

“Dry” scalp

But just tackling the microbes usually isn’t enough – we also need to talk about “dry” scalp.

Your scalp is skin. There’s a bunch of hair and extra oil, but it still has the skin barrier structure, and it’s more comfortable at the right level of hydration. Just like face and body skin, harsh products can dry out your scalp, making it feel itchy and tight. 

Cleansing is one of the biggest issues. Skincare nerds will already know that the wrong cleanser can really mess up your skin.

Related: The Lab Muffin Guide to Basic Skincare 

From a formulation point of view, shampoo is just a type of cleanser. If you use the wrong shampoo, the cleaning ingredients (surfactants) can interfere with the barrier even after rinsing, making it leaky. Water escapes more easily, and irritants enter more easily too – both of these lead to itching.

You might dry it out further with your habits: very hot showers, hot blow dryers, exposure to dry and cold weather, heaters. Hormones can also contribute to dryness (e.g. oil production tends to drop after menopause).

“Dryness” can still be an issue if your scalp is oily. This is similar to how oily skin can still lack water (sebum isn’t a great moisturiser), leading to an oily-but-dry situation.

Why it’s so confusing

You might see the big problem here…

If your scalp issues are caused by microbes but you think it’s dry, you might wash your hair less and put oils on your scalp. But these will make the microbes grow more, and worsen your itching! And if you’re using an anti-dandruff shampoo at the same time, you might think it’s not helping.

So you really need to work out which causes apply to you.

The microbe situation is more common, and it’s even more likely to be the cause:

• If you’ve ever had dandruff before (about half the population is prone to dandruff, and we’re more likely to have an itchy scalp)
• If your scalp or skin is generally oily
• If you don’t wash your hair that much
• If you live somewhere humid

“Dry” scalp alone (without microbes) is less common, but it’s more likely:

• If you and your close relatives have never had dandruff (genetic susceptibility is a big part of dandruff)
• If your skin is very dry (or you might even have eczema)
• If you wash and dry your hair regularly

People with microbial imbalance can also have problems with “dry” scalp, especially since the microbes produce substances that disrupt the barrier, and many dandruff treatments are harsh – it’s a vicious cycle.

Luckily, there are lots of products and tips that work for one, without making the other one worse. But before we talk about products, we need to look at the last piece of the puzzle…

Unidentified allergens

Shampoos contain some common allergens, which can make your scalp itch. 

A cosmetic chemistry insider tip: wash-off products like shampoos are formulated differently from leave-on products like moisturisers. Since they don’t stay on your skin for long, wash-off products have lower risk of absorption, so it’s generally safe to put higher levels of ingredients in them… except for allergens, for people who are allergic to them.

I really need to stress this: if you’re not allergic to an ingredient, you don’t need to avoid it. Allergies are, by definition, your immune system overreacting to a normally safe substance.

But if your scalp itches after using particular products, it can signal an undiagnosed allergy.

Two big allergens common in shampoo are methylisothiazolinone (MI) and methylchloroisothiazolinone (MCI) – these are even nicknamed “the itchy Ms”.

These preservatives became more common after many brands started removing parabens from their products, because of misinterpreted research linking them to breast cancer (they’re actually very safe). Brands still needed preservatives to stop products from going mouldy, so MI and MCI started popping up in products more despite the relative lack of research – and it turns out, a lot more people are allergic to them.

Related post: Propylparaben in CeraVe: Debunking TikTok misinformation

On PubMed, I found 23 articles with the word “epidemic” in the title to describe how much MI and MCI allergy there was. This is very strong language for science papers!

Again, if you’re not allergic, these aren’t a problem. But it’s estimated that a few percent of the population are allergic to these, including me. Even more annoyingly, they’re pretty common in scalp shampoos – it’s improved since I first looked, but MI or MCI are still in a lot of shampoos specifically for itchy scalp.

There’s a related preservative (benzisothiazolinone) that’s super common in liquid laundry detergents. If your clothes make you itchy when you use the wrong detergent, there’s a good chance you’re also allergic to MI and MCI.

Other common allergens:

• Quaternium-15
• Imidazolidinyl urea
• Diazolidinyl urea
• DMDM hydantoin
• Iodopropynyl butylcarbamate
• Fragrance components (e.g. geraniol, citral, linalool)
• Cocamidopropyl betaine
• Propylene glycol, butylene glycol

If a lot of shampoos make you mysteriously itchy, you might want to look into whether they contain these. Patch testing with a medical doctor is the most reliable method, but if you may be able to see some patterns if you keep track of products that do and don’t make you itch.

Note: There are other causes of itchy scalp, but these three are the most likely if it’s something you’ve been dealing with for a long time, and there aren’t any new rashes or other sudden changes (if there are, see a doctor).

Fixing itchy scalp: microbial imbalance

Now that we know the main causes of itchy scalp, and how to work out which ones you have, let’s talk about fixing it – starting with microbe issues.

Anti-microbial actives

If there’s one big takeaway here, it’s this: you don’t need to have dandruff to benefit from anti-dandruff products. Many people overlook these because they don’t have flakes, and for some weird reason, the sensitive scalp products usually aren’t near the anti-dandruff products.

The 4 heavy hitting ingredients for controlling Malassezia:

Selenium sulfide

This is very effective. It’s orangey-yellow, and smells a bit like rubber. Some people don’t mind the smell, but my nose is super sensitive to sulfur (I worked with a lot of sulfur compounds in the lab).

The best smelling ones I’ve tried are the Dercos Anti-Dandruff DS shampoos. Selsun is another popular brand, but the fragrance is a bit strong for me.

Zinc pyrithione

This is another big hitter that works really well. Head & Shoulders pioneered a lot of its use, and it was their main active ingredient for a long time. The main downside is that it’s insoluble, and the tiny particles can make your hair feel a bit gritty.

Zinc pyrithione was recently banned in the EU, even though it was found to be safe at under 1% (note that this means it still shouldn’t be harmful at 100% – I talk more about safety assessments here).

Related post: US Sunscreens Aren’t Safe in the EU? The Science

The EU has decided to pre-emptively ban ingredients with potential CMR health effects, even when safe use levels are found. This is a regulatory quirk, so it’s still available in other countries, notably the US.

Australia is too small to have many of its own formulations, so it’s basically gone here too. I only found a single shampoo with zinc pyrithione in store (Cedel Anti-Dandruff Shampoo. But we can still get zinc pyrithione products through iHerb:

Piroctone olamine

This is a newer ingredient that’s getting more popular. It’s soluble and doesn’t smell, so piroctone olamine shampoos look and feel like normal shampoos.

I was actually using one for ages without realising: Essano Scalp Refresh Shampoo. I was amazed that I could go three days without feeling itchy (usually it’s just a day, sometimes less – my scalp is super fussy).

In most countries outside the US, there are a huge range of options with piroctone olamine – I found it in tons of scalp products when I went looking, including many that didn’t say dandruff. Some other shampoos I’ve enjoyed using:

Ketoconazole and climbazole

Ketoconazole is an antifungal that’s most commonly found in Nizoral products. The weaker cosmetic version is climbazole, which is in a lot of Dove shampoos.

Some Malassezia species are resistant to azoles, so if it doesn’t work for you, it’s worth trying a different active. The other three actives also have broader antimicrobial activity which might be useful for scalp acne.

Other dandruff ingredients

Some other ingredients for dandruff aren’t as effective for controlling Malassezia, but they can help with other aspects like flakes (salicylic acid, coal tar) or soothing your scalp (menthol, rosemary, peppermint, tea tree oil). Check the ingredient list to see which one you’re getting.

Tips for using anti-dandruff shampoos

1. Not all shampoos are equally effective

The formula isn’t just about the active ingredient percentage, so don’t dismiss an ingredient just because one product didn’t help! A clinical testing claim is a good sign that the formula’s been tested and optimised (e.g. “6 weeks anti-dandruff relapse”, or “up to 100% dandruff protection”).

2. The shampoo needs to be massaged into the scalp

The microbes are on your scalp and they mostly live inside the hair follicles, so you want to focus on getting the shampoo to cover your scalp as much as possible. In general, the lengths your hair don’t need to be shampooed as much.

3. Follow the instructions on the bottle

There’s a common myth that anti-dandruff shampoos all work better if you leave them on for a few minutes. But this only works for some shampoo formulas!

For example, anti-dandruff shampoos commonly have their active ingredients wrapped up in little bubbles (called a coacervate system) that only deposit when you dilute it with water, during rinsing. Leaving these formulas on your scalp for longer might just increase irritation and itching, for no good reason. 

The delivery system depends on the overall formulation, not which active it contains. The instructions should tell you how best to use it.

4. Be careful with conditioner

If you use a conditioner without anti-dandruff ingredients on your scalp afterwards, you’ll actually wash away some of the actives. So either keep the conditioner on the lengths of your hair (below the ears), or condition with an anti-dandruff conditioner.

5. Shampoo regularly

This means you’re applying more anti-dandruff actives, as well as getting rid of the oils that feed microbes, any irritating substances, and the microbes themselves.

6. Use an anti-dandruff serum if needed between washes

You can also get anti-dandruff ingredients in serums. These are great between washes, although they don’t really replace proper shampoo.

My favourite is Dercos Anti-Dandruff Serum 10, which has piroctone olamine as well as a bunch of antioxidants, and soothing madecassoside (from centella). It doesn’t leave any sort of stickiness or weigh hair down – after it dries, I can’t tell I’ve applied anything. The nozzle also makes it easy to aim at the scalp.

Some anti-dandruff serums:

• Zinc pyrithione:
• Piroctone olamine:

Moisture

If microbes are your issue, you’ll also want to be mindful of moisture. A damp scalp can make it easier for microbes to multiply.

Drying the hair around your scalp faster after washing can help. Use a hair dryer rather than air drying your hair, especially if it’s cold or humid.

To protect the scalp barrier, don’t use a setting that’s too hot. My Panasonic hair dryer has a scalp mode that’s the perfect temperature, but hopefully your hair dryer has a setting that feels comfortable. If it’s too hot, hold the dryer further away.

Hats and helmets can also trap moisture and make things worse, especially if you sweat. Try to have some airflow, and wash your hair soon after sweating.

Fixing itchy scalp: “Dry” scalp

Onto some tips for dry scalp, which is also important if you have a microbial imbalance.

Use gentle shampoo

Like for your face skin, you want to use a shampoo that doesn’t make your scalp feel stripped and dry. Harsh shampoos also make it easier for irritating substances to get in and cause itching.

There are lots of gentle anti-dandruff shampoos these days. If you’re using regular shampoos instead, or in addition to those, this is also important. In general, a slightly acidic, skin-friendly pH is gentler for your scalp (roughly pH 4 to 7).

Avoid using conditioner on your scalp

The surfactants in conditioners are actually more irritating than the ones in shampoo. The hair near your scalp is nice and undamaged, so it doesn’t need much conditioning.

Antioxidants

Skincare ingredients can also be beneficial for your scalp. Antioxidants are a safe option for protecting against irritation, and improving the condition of the scalp:

Many anti-dandruff serums include antioxidants, as do many general scalp serums – just make sure they don’t have oils in them if microbes are an issue.

Water quality

Tap water can be a big issue in some places, especially hard water which contains dissolved metal ions (there might be chalky water stains and build-up around your taps). Hard water can irritate your skin and scalp, and make your hair feel like there’s a film on it. Some metal ions can also speed up oxidation.

The best solution is a whole house water softening system, but there are also in-line softening systems you can get just for the shower. “Filters” usually get rid of chlorine but not hard water ions, so make sure you check what exactly the product is going to do before you buy it.

Products I don’t find helpful

Oils

If microbes are part of your problem, you want to be very careful with oils. Malassezia feed on oils, it makes them grow faster and it’s what they turn into irritating substances, which make your scalp more dry, irritated and leaky. Plant oils are particularly bad – I’d recommend avoiding leave-on scalp products with plant oils entirely.

Most oils actually aren’t that good at sealing water into your skin or scalp. Some people find oils helpful, but I think it’s mostly the fact that massaging helps get residue off the scalp, especially if you use a lot of product and don’t wash your hair that often. If you’re in this category and think you might have this microbe problem, maybe try massaging a serum with anti-dandruff ingredients into your scalp instead – the Head & Shoulders Royal Oils products are designed for this sort of use.

Dry shampoo

This can be helpful for soaking up oil and removing some of the irritating substances from your scalp, but it can’t really replace actually washing your hair. I see a lot of people who should shampoo more, trying to spray on more and more dry shampoo! Also, spraying too close can dry out your scalp.

Scalp scrubs and brushes

This is really personal preference, but I don’t find them helpful for my hair type and routine. I find it pretty difficult to get scrubs to reach my scalp and it feels like it’s mostly scrubbing the hair itself, which is extra damage I don’t need.

I don’t mind silicone scalp brushes, but I have nails which work fine.

Chemical exfoliants

This is a similar situation – chemical exfoliants might be helpful if you have a lot of buildup. But since I wash my hair every day and I don’t use much product, they haven’t made much difference for me. I know many people like using The Ordinary’s budget-friendly Glycolic Acid 7% Toning Solution for this, which also has a nozzle for aiming.

References

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Dawson TL. Malassezia globosa and restricta: breakthrough understanding of the etiology and treatment of dandruff and seborrheic dermatitis through whole-genome analysis. J Investig Dermatol Symp Proc. 2007;12(2):15-19. doi:10.1038/sj.jidsymp.5650049

Gordon James A, Abraham KH, Cox DS, Moore AE, Pople JE. Metabolic analysis of the cutaneous fungi Malassezia globosa and M. restricta for insights on scalp condition and dandruff. Int J Cosmet Sci. 2013;35(2):169-175. doi:10.1111/ics.12022

Jourdain R, Moga A, Vingler P, et al. Exploration of scalp surface lipids reveals squalene peroxide as a potential actor in dandruff condition. Arch Dermatol Res. 2016;308(3):153-163. doi:10.1007/s00403-016-1623-1

Jourdain R, Moga A, Magiatis P, et al. Malassezia restricta-mediated lipoperoxidation: a novel trigger in dandruff. Acta Derm Venereol. 2023;103:adv00868. doi:10.2340/actadv.v103.4808

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Schwensen JFB, Uter W, Aerts O, et al. Current frequency of contact allergy to isothiazolinones (methyl‐, benz‐ and octylisothiazolinone) across Europe. Contact Dermatitis. 2024;91(4):271-277. doi:10.1111/cod.14641

Reeder MJ, Warshaw E, Aravamuthan S, et al. Trends in the Prevalence of Methylchloroisothiazolinone/Methylisothiazolinone Contact Allergy in North America and Europe. JAMA Dermatology. 2023;159(3):267-274. doi:10.1001/jamadermatol.2022.5991

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Davis MG, Piliang MP, Bergfeld WF, et al. Scalp application of antioxidants improves scalp condition and reduces hair shedding in a 24-week randomized, double-blind, placebo-controlled clinical trial. Int J Cosmet Sci. 2021;43 Suppl 1:S14-S25. doi:10.1111/ics.12734

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